Original post:

You folks have nearly saved my life with furnace advice last winter, and some of you know who you are because I did as I promised and made it up to you afterward. For that I’m still grateful.

Tonight is the coldest it’s been here since last winter, about 5 degrees Fahrenheit. Wind is calm to none. Not sure if those elements come into play.

Heat is forced hot water, oil heated by a Weil McLain Gold Series furnace.

Within the last hour I’ve heard the furnace doing something I’ve never heard before at any time. The best I can narrow it down to is a rattling from the air intake tube (for lack of a better term). It begins just over one minute after the furnace begins to run, then slowly gets louder. Eventually it reaches its full volume and stops when the furnace stops.

I’ve put my ear up to where the air intake enters the motor-looking thing (large black box) and it seems that’s where the noise comes from. The noise changes if I gently move the air intake tube.

Any ideas? Worn out air intake motor? Something I can hopefully fix by myself?

Thank you for reading this.

Update:

Woke up to a cold house. Furnace trouble light, little LED near the manual restart button, was blinking. Pressed once and the furnace started and ran like normal for about five minutes. Then the noise described above started and it shut off. Went to restart and the LED is blinking again. It did restart then the noise began immediately and it stopped. Any ideas? I’m sorry to sound so desperate but we don’t have much money and it would be very difficult to call someone to come and repair this. Thank you all so very much!

Open it up and have a look inside if you are halfway competent.

Mine sounded like it was going to go into orbit, but the blower sucked the paper schematic off the cover and was chewing it up in the squirrel cage.

May be something simple, may be something requiring pepper for angus.

Check the easy stuff first.  Shut-downs are usually over-temperature events or other safety-related function kicking in.  So, if an airway is blocked or a blower/pump isn't working properly,... click! and it goes off.

Do you have the schematic?

Pictures would greatly help.
Maybe a video of the noise.
Could be something dumb as a loose squirrel cage on the shaft of the motor, loose motor mounts, etc.
if you can touch the intake tube, and you can control the noise, I’d start there. Turn off the unit, and open it up. It’s not rocket science, take your time, take pictures for your personal reference throughout everything, if you take anything apart, take detailed pictures and maybe write things down on a paper as notes what you did. The design is fairly simple and anyone that can use a wrench or screw driver for basic homeowner things should be able to dig into it.
Diaging electrical issues and fuel problems will require more skill and tools. But start with the intake tube. And what that is attached to at the burner. Check for play, loose nuts/bolts. Check the shaft bearing by jiggling the shaft up and down left right. Should be tight and no play. The shaft may slide in and out from the motor a whisker. A blade from the squirrel cage could be broken due to the awesome quality control of products nowadays causing a imbalanced blower, which will loosen nuts bolts, ruin the bearing, and could bind up. Just an example.
But if you can control the noise by touching and moving the tube, it’s in there.
If I remember correctly, the blower in the oil burner runs the oil pump as well with a direct drive from the shaft. Pretty basic stuff. But start simple. Don’t jump to conclusions.

OK, we have an update for the moment.

Lesson learned: listen to the pros when they give you free advice.

Thank you all for the responses above! I've had to balance work and home quite delicately today so I haven't been on here as much as I hoped.

My wife knows someone who does plumbing and heating for a living. I spoke to him on the phone and he insisted I check to see if the fuel line froze (as it did last year, almost exactly to the day). I bled the system and observed steady fuel flow but it was foamy and the furnace wouldn't stay running. I figured that the fuel couldn't be frozen and I strongly believed the problem involved the air intake as that's what it sounded like was making the strange noise. My wife's friend said that all he could do over the phone was recommend I treat the situation as if the line was frozen, and no matter what he couldn't stop by today.

Wouldn't you know, I went outside to the fuel tank, opened the filter housing at the tank and dropped the filter to check for flow...and it was a trickle. Five minutes with a heat gun and it was flowing strong. Went back inside, bled once more, and that was over an hour ago with the furnace running just fine. The gentleman who helped me said that for now he believes I heard the fuel pump trying to compensate for the poor flow. He will be coming over next week to give the whole system an inspection.

Good one!  
As dumb as it seems, each year everyone should get a tune up. The filters hold a lot of the moisture as well and should be changed. Also, with good oil delivery company’s, they will treat the fuel with additives to help with moisture, fungus, and antigell. So sometimes, SOMETIMES, the little bit higher priced guy has better quality of oil. You should use diesel antigell additive before they come and fill you up next.