Cliff notes version : Began having an audible rattle on first floor and furnace is located in basement.  Messed around with it and found  when I removed one of the two filters (14*25; side by side) the noise and rattling abated.

Replaced old filters with new and problem returned. Figured it was an air flow issue and checked that all cold air returns were clear. Problem was still present. I pulled the cover and and vacuumed out the blower the best at could, with no change. At the point I call in a relative who owns a heating company (did all the HVAC work at my previous home and has always been great.) and discuss problems with him over the phone. He seems to think something is stuck in the blower and comes over to see as was on a 48 hour shift. Pulls blower  washes, etc according to wife.

Problem never really goes away and when I get home today it's doing it again... This time I switch the Thermostat to ON instead of AUTO and the issue largely goes away

Other factors:

Upstairs has seemed colder and warm air flow seemed reduced.

In the ON position, the slide door drape billows. On AUTO it just sort of quivers.  

Furnace is a Rudd Deluxe 80 Plus, unsure when it was installed


UPDATE:

Noise is still annoying me, shot a video to see if that helps. Not sure of I should by a new motor or fan first.

Bad bearings at the fan?  Heat changes tolerances...  HVAC guys, your opinion??

Depending on the furnace it could be running two different speeds for heating and constant fan.  Could be a dirty blower or failing bearings.  If you grab the motor shaft (with the breaker off and the blower not spinning) and wiggle it up and down, back and forth there should be no play.  In and out there may be a little, which is okay.  If you have any up and down, back and forth you need a new blower motor.

This, two different blower speeds. heat is low/med low for auto, high when in on position. Have the filters been replaced lately with more restrictive filters that create to much air restriction? When they are removed, it goes away so it can definitely be a air flow issue.

One thing I would check is the capacitor if the motor is a split type. A bad cap can cause the motor to never get up to speed and be noisy. It needs to be +-6% of the rating. Good thing is that are dirt cheap and easy to replace.

Could be a piece of debris on the wheel. Check bearings or resilient mount.

Thanks for the replies.

I'll Google the capacitors and report back

Update:

I finally got sometime to devote to getting to the bottom of the problem. As soon as I popped the bottom panel I saw the whole blower assembly was very loose in its hanger. I could very easily shake the entire assembly. The drum spun easily with no audible noises when manually spinning. I pulled everything out and checked to see if the motor had any play and found none. I moved on to the capacitor and realized my cheap Harbor Freight Multimeter doesn't read microfarad, but worst case I can source one locally for $12. While I had it out I rewired the motor from low, to medium-low.

When I put everything back together there was still a lot of play in the  assembly so I cribbed it with a scrap piece of wood.

That took care of a large portion of the noise.

Thanks for all the suggestions.

Update in OP....looking for suggestions. The noise is annoying the shit out of me. Priced a new motor and blower assembly and would rather not spend $300 bucks on an old furnace.

Very possible the blower wheel has gone out of balance or a weld has broken. While motors can be noisy, severe vibration can usually be traced back to a bad wheel or loose motor mount. Sometimes the blower housing can crack but that isn't too common.

$300 isn't much in the furnace repair world, A small inducer/ventor assy for a York cost me $227 wholesale cost today and retail is double that. Then I priced a rubber 2.5 x2.5 inch vent coupling for an old Bryant furnace, $142 bucks and not available. [think Furnco type coupling]

Did he try and spin the motor shaft when he had the fan off?


It is often easy to feel a bad bearing if you just spin the shaft with your fingers.

Or even a pair of pump pliers if you need some grip.

Be careful not to mar the shaft surface or the fan may be hard to replace.

I'm not sure if I spun it... I checked to see if it had any lateral play and nothing seemed off. I'm going to pull them and see what I can figure out on Sunday. Thanks for all the advise