I have a 2000 Wrangler sport (manual tranny) with ~63k miles on it.  For a little while now I have heard a noise coming from the rear end when I accelerate slowly.   Driving with the window down today I confirmed that it is definitely coming from the rear part of the vehicle (my girlfriend, who I just dropped off, concurs).  It's hard to explain, but similar to the "lugging" noise the engine makes if you give it too little gas and too much clutch, only more apparent and more metallic.  I tried to reproduce it but couldn't.  I've noticed the noise before.  All times it is when I am accelerating slowly (such as in a parking lot or crowded highway).

I would greatly appreciate any tips to diagnose the problem and at least identify some starting points to give to the mechanic.  It hasn't been offroading, but there are some mean speed bumps in the parking lot at work and home.  Hope this helps.  Many thanks for any tips.  Hoping it's nothing big.

I'm thinking it might be excessive backlash between the ring and pinion gears in the rearend.  Does it have a howl to it at highway speeds?  Could also be u-joints on the drive shafts.  A good mechanic should be able to trace the problem rather quickly.

have your U Joints checked for play...  

My one ton GMC's rearend has been whining for 6 years..  I changed the gear lube,
and bought an additive for it (by slick 50)  and drive it.. I know it will go someday..  but
it's been over 6 years now..  I bought a complete used dually rear end for when it does..

There is a service bulletin for "Gear Train Noise When Manual Transmission Is In Neutral"

An Excerpt....

"The customer may experience a transmission gear train sound when the engine is at idle and the transmission is in neutral with the clutch released. The sound may be described as a light gear rattle or gear growl. The gear train sound may appear to be coming from the transmission shifter and/or center console area. The sound may be more noticeable in higher ambient temperatures or as the transmission reaches its operating temperature. The gear train sound enters the passenger compartment by way of the transfer case range lever linkage. A revised torque shaft has been released to improve the isolation of the gear train sound."


If this sounds like the problem you are experiencing, I can email the entire service bulletin to you.

I hope you find your problem.

does it have a limited slip differencial?

Could be U-joints, Could be your tires, inflate them to normal recommended pressure when cold.  Could be rear hub bearings or the slip yoke on your drive shaft.  This should have a grease fitting on it.  Try lubing it first to see if it'll go away.  Sometimes they'll stick a little and make noise as they move forward and backward when you start and stop.  It could also be your brakes,  You make need to replace or adjust them.  Also check you gear oil level to make sure there's enough in there.  You could also have it changed and have some additive added in that'll make the clutches in it quieter if you have a limited slip rear end.

You might try jacking the rear end up and with the transmission in neutral and the park brake off (chock the front wheels fore and aft) feel for axial play in the wheel bearings and check for fluid on the brake backing plates or caliper mounts. Then check the U-joint and yoke for security and condition. If the noise is comming from the differential carrier or ring and pinion the rear end is DOA or soon will be. Planerench out.

Okay, forgive me as I'm learning.  I learn quickly, though.  

No howl or other odd noises at any speeds.  I have read several suggestions to check the U-joints for similar noise descriptions on Jeep sites, and will check that.

Interesting that you mention backlash.  I looked it up and finally found out what it is.  I have had issues previously that I could only describe as excessive play in the transmission.  If I didn't play the clutch just right it felt as though the gears/transmission would "bounce" causing the Jeep to lurch/bounce.  Could this be a further indicator, cause, etc...?

Thanks for your help.  I'll keep an eye here and will take it in for a look next week.

Quoted: There is a service bulletin for "Gear Train Noise When Manual Transmission Is In Neutral" An Excerpt.... "The customer may experience a transmission gear train sound when the engine is at idle and the transmission is in neutral with the clutch released. The sound may be described as a light gear rattle or gear growl. The gear train sound may appear to be coming from the transmission shifter and/or center console area. The sound may be more noticeable in higher ambient temperatures or as the transmission reaches its operating temperature. The gear train sound enters the passenger compartment by way of the transfer case range lever linkage. A revised torque shaft has been released to improve the isolation of the gear train sound." If this sounds like the problem you are experiencing, I can email the entire service bulletin to you. I hope you find your problem.

Thanks!  I have seen this before, and actually tried to see if I could hear it.  There is a bit of a noise in the condition noted here, but being used to a manual vehicle I wasn't concerned.  It struck me as normal no-load noise.

My problem is while the vehicle is in gear (first gear) and accelerating somewhat slowly from a full stop.

Quoted: does it have a limited slip differencial?

[ashamed]  I don't know.  It's "stock" so I would say no.

Quoted: Could be U-joints, Could be your tires, inflate them to normal recommended pressure when cold.  Could be rear hub bearings or the slip yoke on your drive shaft.  This should have a grease fitting on it.  Try lubing it first to see if it'll go away.  Sometimes they'll stick a little and make noise as they move forward and backward when you start and stop.  It could also be your brakes,  You make need to replace or adjust them.  Also check you gear oil level to make sure there's enough in there.  You could also have it changed and have some additive added in that'll make the clutches in it quieter if you have a limited slip rear end.

Tires pressure is good and monitored regularly.  I'll take a look at the U-joints, though I'll admit I don't know what I'm looking for.  I'll check the service manual (I plunked the money for one when I got the Jeep figuring it might be a good investment).  Brakes should be good, as front were replaced recently and rear were checked (just had the 60k check).

Lots of stuff to check.  I think I'm best off to visit the mechanic and take him for a short ride.

Yes your 2000 Wrangler Sport has a limited slip differential.

Greasing the u-joints will eliminate them as a suspect.

Take a piece of garden hose and duct tape it to the differential cover on the rear axle and run the hose
up into the cab. As you drive, listen through the hose to assure if the noise eminates from the rear axle.

Follow Planerench's advice also to find the source of the noise.

HS1

I had a 89 jeep pick up that lost a tooth in the rear end. It would make a clunk sound every now and then. I knew something was wrong when both tire spun in the dirt and I didn't have limited slip. You can pop off the rear diff cover and check the gears. 1/2 hour job.

Quoted: Also check you gear oil level to make sure there's enough in there.

Never overlook the obvious!

Also, if it has ever been in water, the gear oil could be contaminated with water, dirt, etc. New oil (along with any recommended additives) would definately be a good first step.

I don't know about the TJs but the YJs were know for bad U-joints.  It took 80k miles but my drive shaft finally gave and dropped out onto the street on my way home from work.  Thank goodness for 4 wheel drive.  For about 10 miles I had a front wheel drive Jeep.

Mechanic noted the noise is coming from the gearbox, and asked about the differential and transfer case fluid.  It hasn't been changed (60k miles on the Jeep).  They suggest changing it every 30k.  It was cheap enough to do, and I feel a difference.  No noise yet (but only been a day).

They sorta don't mention those fluids in the maintenance schedule that I've seen.  Maybe I missed...the "heavy use" schedule suggest draining and refilling axels at certain points, but the normal maintenance schedule does not.  Is this something that should be done occasionally?  Any other items they "forget"?

Quoted: Mechanic noted the noise is coming from the gearbox, and asked about the differential and transfer case fluid.  It hasn't been changed (60k miles on the Jeep).  They suggest changing it every 30k.  It was cheap enough to do, and I feel a difference.  No noise yet (but only been a day). They sorta don't mention those fluids in the maintenance schedule that I've seen.  Maybe I missed...the "heavy use" schedule suggest draining and refilling axels at certain points, but the normal maintenance schedule does not.  Is this something that should be done occasionally?  Any other items they "forget"?

Both my 2001 Ranger and my wifes 2004 Explorer are 4WD.  I change out the gear oil in the axles every 2yrs/24K and use 100% synthetic Amsoil gear oil and in the rear axle of the Ranger I use the Amsoil additive for limited slip axles for its TracLok axle.  I change out the transfer case fluid annually (they both use 3qts of ATF, so I use Amsoils syntetic ATF).  I also flush the transmission (both automatics) annually and use Amsoil ATF.   I manually flush the brakes myself every year at home.  I also change the power steering fluid out manually at home and replace it with Amsoil ATF.  This all maybe overkill but these vehicles are daily drivers and are driven in the terrible stop and go driving around here and I've never heard of having 'too clean' of fluid.  I typically use Amsoil or Mobil 1 0w30 oil and change it every 4-5K.  I have a kit for each vehicle but haven't installed them yet that will allow the oil to last 1yr/35K because it's a bypass filter and filters down to 1 micron.

If the noise goes away when you shift the trans into 4th, the noise is coming from your transmission.

Pull the steering wheel off, and buy another Jeep, then put your old steering wheel on the new Jeep, Problem SOLVED........

Quoted: Mechanic noted the noise is coming from the gearbox, and asked about the differential and transfer case fluid.  It hasn't been changed (60k miles on the Jeep).

What, you wish to have to replace your entire drive train?     Other than brake fluid & perhaps power steering fluid (sometimes it too) ALL fluids should be changed on a Jeep. Front & rear diffs, tranny, tranfer case (two different fill holes, btw) everything.

As long as it's kept topped off, I usually change mine every 50Kor so.

Wrangles don’t usually have the problems that the GC do with the Dana 44 type diff's (Front Or Rear)
I have seen a few Wranglers with axle bearing problem which transmits to the gears through the axle , usually a grinding type noise or low rumble . Pinion bearing or gear problems usually show up as a whine on acell or decell only , coast noise is usually case bearings at first that progresses to a clunk/snapping noise under load . U-joints squeak at first then develop a clunk when changing directions ( Forward to Reverse ) and because of the short steep angle rear drive shaft in a wrangler they usually cause a vibration too . Last but not least is the splined slip joint in the rear drive shaft which usually makes a metallic pinging or snapping noise .  All of these problems are usually easily pinpointed with a test drive and/or running it on a lift in the air .

Quoted: Mechanic noted the noise is coming from the gearbox, and asked about the differential and transfer case fluid.  It hasn't been changed (60k miles on the Jeep).  They suggest changing it every 30k.  It was cheap enough to do, and I feel a difference.  No noise yet (but only been a day). They sorta don't mention those fluids in the maintenance schedule that I've seen.  Maybe I missed...the "heavy use" schedule suggest draining and refilling axels at certain points, but the normal maintenance schedule does not.  Is this something that should be done occasionally?  Any other items they "forget"?

Always go with the severe duty maintainence schedules.

After the front & rear diff fluid and tranny case fluid was flushed I'm still hearing the noise.  A second trip to the mechanic resulted in another diagnosis of the noise coming from the "gear box", and he referred me to dealer service since he doesn't do trannys.

I took it to Tyson's Jeep today and paid them $30 to tell me I need my 60k checkup including changing all diff fluids and tranny fluid.  I would imagine it's hard to miss the difference between 30/60K differential fluid and 2-3k differential fluid (and definitely not hard to tell the spark plugs, air filter, etc... have been replaced recently), I concluded any further work there would be a waste of money.  I did challenge the guy to explain how they determined the cause is the differential fluid.  "The car has 60k miles on it.  It's time for the 60k check-up and a diff fluid change.  We see this all the time."  Okay, what about the fact I just had the fluids changed?  "Oh, they probably don't know about 'the additive'".  Uh huh.

I've decided I need to figure the problem out myself.  I don't want to let it linger in case it's a $200 issue that will soon turn to a $$$k tranny rebuild.  I also don't want to spend hundreds of dollars going to every mechanic in the area trying to diagnose the problem with the "let's try this" method.

I'll try the above suggestions given the space and tool limitations I have.  I do have a service manual which I'm sure will come in handy.  

Quoted: Last but not least is the splined slip joint in the rear drive shaft which usually makes a metallic pinging or snapping noise .  All of these problems are usually easily pinpointed with a test drive and/or running it on a lift in the air .

What is this guy (splined slip joint)?  That sounds like the problem I'm having, maybe.
1. Happens only when accelerating from a dead stop
2. Noise/feeling occurs just as clutch really takes hold and Jeep starts to move
3. Either feels like the tires are spinning, as if gravel under tire on asphalt road, or LOUD noise like someone hanging on undercarriage and banging on drive shaft with wrench (mettalic pinging/knocking)
4. Noise/feeling continues until clutch has fully engaged and car moving; Yes, noise frequency increases (more rapid) as car starts to move...several knocks, not just one.
Not sure if it happens in reverse.  No other unusual noises during driving, idle, etc...

Thanks for all the help, guys!  It's frustrating to diagnose and bothersome thinking about the systems (and possibly money) involved.  I'll let you know what I find.  Searches haven't turned up a lot of good info yet.

Quoted: After the front & rear diff fluid and tranny case fluid was flushed I'm still hearing the noise.  A second trip to the mechanic resulted in another diagnosis of the noise coming from the "gear box", and he referred me to dealer service since he doesn't do trannys. I took it to Tyson's Jeep today and paid them $30 to tell me I need my 60k checkup including changing all diff fluids and tranny fluid.  I would imagine it's hard to miss the difference between 30/60K differential fluid and 2-3k differential fluid (and definitely not hard to tell the spark plugs, air filter, etc... have been replaced recently), I concluded any further work there would be a waste of money.  I did challenge the guy to explain how they determined the cause is the differential fluid.  "The car has 60k miles on it.  It's time for the 60k check-up and a diff fluid change.  We see this all the time."  Okay, what about the fact I just had the fluids changed?  "Oh, they probably don't know about 'the additive'".  Uh huh. I've decided I need to figure the problem out myself.  I don't want to let it linger in case it's a $200 issue that will soon turn to a $$$k tranny rebuild.  I also don't want to spend hundreds of dollars going to every mechanic in the area trying to diagnose the problem with the "let's try this" method. I'll try the above suggestions given the space and tool limitations I have.  I do have a service manual which I'm sure will come in handy.   Quoted: Last but not least is the splined slip joint in the rear drive shaft which usually makes a metallic pinging or snapping noise .  All of these problems are usually easily pinpointed with a test drive and/or running it on a lift in the air . What is this guy (splined slip joint)?  That sounds like the problem I'm having, maybe. 1. Happens only when accelerating from a dead stop 2. Noise/feeling occurs just as clutch really takes hold and Jeep starts to move 3. Either feels like the tires are spinning, as if gravel under tire on asphalt road, or LOUD noise like someone hanging on undercarriage and banging on drive shaft with wrench (mettalic pinging/knocking) 4. Noise/feeling continues until clutch has fully engaged and car moving; Yes, noise frequency increases (more rapid) as car starts to move...several knocks, not just one. Not sure if it happens in reverse.  No other unusual noises during driving, idle, etc... Thanks for all the help, guys!  It's frustrating to diagnose and bothersome thinking about the systems (and possibly money) involved.  I'll let you know what I find.  Searches haven't turned up a lot of good info yet.

There is an friction modifier additive that is needed for 'posi' or limited slip axles.  My Ford Ranger has a 'Trac-Loc' axle (Fords name for limited slip) when I changed to Amsoil Series 2000 gear oil Amsoil said that sometimes you need the additive but to see if you can run without it (better mileage apparently if you don't use it).  Well about 2 days after changing the gear oil without using the additive the axle would 'chatter' when turning left mostly but sometimes turning right too.  Really uneasy feeling, it felt like the trans was bad or something.  I then bought their brand of additive and added it.  It took a few days to work itself in to the gears but now it doesn't chatter when turning at all.

I don't think the additive is your problem.   Possible but not very probable.  Since yours is only giving you that symptom in a straight line from acceleration I'm thinking its the driveshaft, U-joint, slip yoke or possibly the pinion gear.  If your slip yoke has a grease fitting see if you can grease it.  Have you ever had your clutch adjusted?  My 81 CJ7 had an adjustable mechanical clutch, I don't know if they're still using mechanical clutches or hydralic.

Quoted: The dealership guy was an idiot rather than a good service writer.  Look elsewhere for good service.

Add "lazy" and I'll say you have it 100% correct.  I forgot to mention that changing the front and rear diff and transfer case fluids would have cost over $300 there?  Geesh.

WIsh I could hear your problem as I it should be rather easy to figure out.  I kinda suspect the clutch but hard to say without better description.  If you like I can do the 20 questions bit and try....

I thought about the clutch because of the "slipping" feeling, but can't work out in my head why it would also make a loud knocking noise.  Feel free to go the 20 questions route, either on here or IM me for a personal e-mail address.  We're only limited by your patience.  

Forgive me in advance for not being up to speed on the latest in automotive technology.   I currently have no idea what some of the stuff mentioned does.  But rest assured I have enough aptitude to figure it out in short order...I just need to reference the pictures.

I just had a similar circumstance with my Jeep. I had taken my Jeep in for service and to get the sending unit replaced and the dealer noticed that my Jeep had a broken exhaust pipe bracket, so he fixed that as well. When I got it back, I would hear the metallic noise that you described when dropping down to low speeds or at idle when I revved the engine. It turned out it was the exhaust pipe bracket that was vibrating at low speeds and hitting the frame and/or gas tank skid plate. The shop lowered the bracket and it seems to have solved the problem. May not be what is causing your problem, but it might be worth taking a look at. When I first heard it, I thought it was U-joints as well, but the dealer had just checked those and ruled them out.

Interesting....  A friend has his Jeep in the garage as I type this for a very similar thing.. (extended warranty or I would have fixed it for him by now)    Although if you havent been off road, it would probably a different reason, unless you lifted it.   His skid plate underneath the tranny was pushed up, (high centered it on rocks a few times)  which knocked the driveshaft angle way off.   This played hell on his pinion bearing..  and it kind of snowballed from there, his rear is toasted.

Reason I mentioned a lift.. If you lifted it and didn't use a t case drop kit, you could run into the same problems.   Also if your mechanically inclined, it is not very difficult to change the gear oil in your rear diff..  While you have the cover off, look for any kind of tell tale signs such as metal shavings. At 63k miles, I would have changed the gear oil anyways.  Another east thing for you to do, find a level place to park, chalk up the wheels, and put the t case in neutral.  then crawl underneath and see if there is any excessive play in your driveshaft or in your U Joints.    It wouldnt hurt to do the above with your front driveshaft and axle too.   Might as well change the gear oil in your trans and tcase also..