Well i recently bought a 91 240. The previous owner told me that the belts squeel from time to time when coming to a stop or idling. But I bought the car anyways because it didnt have much rust and it was pretty clean. When driving it home that night, the squeeling would happen here and there but stopped immediately when i reved to about 3000rpm (it would only squeel sometimes when coming to a stop, never when im cruising). Anyways…After that i let the car sit for about a month because i went to the states a couple days after buying the car and when i came back i turned on the car and the friggen thing squeeled uncontrollably 0.o So i quickly turned my car off and tried again like 3 more times hoping it would just go away. But it didnt. So now i am stuck and have no clue what i should do. Has anyone delt with this before? Trouble shooting tips? Do i have to change the belt? Any help would be appreciated, thanks 
buy a new belt, swap it out, see if it goes away - it should, more then likely the belt is old as fuck and dry like a grannies vageegee. Had this problem on my sr, and on my old pos ford. You can buy belt wax if you dont want to change the belt, but its only temporary.
If it doesnt go away, back to the drawing board.
Thanks, yeah the belt definatly looks pretty bad. I guess ill just have to swap it out and see. Could it be other problems besides the granny belt?
probably not, the belt gets old and dry, they slip on the pulley, and thats the squeal your hearing. Try the belt wax first (comes in aerosol), if it goes away you know thats your problem. But belts are cheap and it wouldn’t hurt to swap em out.
Okay Thanks, ill try that
^ or just use ketchup… i know, redneck fix
mine did that when the water pump bearing was seizing up
^hmm. I’ll keep that in mind. Thanks guys.
try to first just tighten the belt that’s already on it. make sure there is no slop and they are all on good and tight. if it goes away great. still buy a new belt and go to bed happy knowing you spent like 5 bucks.
I am more inclined to think its a bearing. could be any bearing too.
okay, the previous owner said it was fine before but only started happening when it got cold. I just checked the belts and they looked fine to me, no visable fraying or cracks. I think one of the belts have been changed already because one of them doesnt look like a factory belt but i dont know. Also the belts are pretty tight. Ill just replace the belts on my own time and hope for the best. Hopefully thats all i have to do.
Are you sure it’s not your timing chain rattling? How you described it pretty much sums it up… Only noticeable mostly when you turn the car on or the engine is cold, squeels until like 3000 rpm and if your cruising you don’t really hear it at all. Comes back too when you down shift and come to a stop.
How many KM’s are on your car?
I originally thought it was the timing chain rattle but it really doesn’t sound like it. Ive heard that a Timing chain rattle sounds more like marbles in a pop can. This is a different sound. I’m gonna try tightening one belt that feels sort of loose once it gets warmer. Maybe a belt is slipping on a pulley? Since all the pulleys are different sizes. It’s possible that some slipping is happening. Thanks for your input though. Also my car has over 400 000kms 
but the engine was swapped before. Lol but the body has very very little rust.