my 98 M3 has this metallic squeal under *very* light throttle and right when you let off in either 4th or 5th. it will also do it while shifting 3-4 and 4-5. generally between 40-65 mph. not a peep under heavy throttle. the only real way to describe the sound is a chain dragging on the ground.

the noise seems to come from somewhere in front of the doors and from the bottom of the car. over the past few months, i havent noticed it get any louder, but it seems that it happens a bit more easily now.

at first i thought belt. replaced tensioner, belt, pullies..... nothing. so i made it squeal then coasted. both in gear w/ clutch in and in neutral with clutch out and in. it keeps squealing either way.

so i made it squeal again then shut the motor off at about 55 mph to eliminate any of the pulleys or the pilot bearing, TO bearing and input shaft bearing. it still squeals with the motor off while coasting at 50-60ish. it will continue until i slow to about 40 then will disappear.

if you have ANY idea as to what this may be.... for god's sake, say it. this is driving me crazy. :help

Have you considered the possibility that this might be from an intake leak. That would be worst under partial or closed throttle conditions.

i have, but quickly ruled it out after installing an M50 manifold with new gaskets and seals and an RMS stg 1 supercharger. the sound has not changed and is only pretty much speed/load sensitive.

i really wish i could describe the sound better but i ask everyone (before i say anything) what it sounds like and they all say a chain dragging.

so i made it squeal again then shut the motor off at about 55 mph to eliminate any of the pulleys or the pilot bearing, TO bearing and input shaft bearing. it still squeals with the motor off while coasting at 50-60ish. it will continue until i slow to about 40 then will disappear.
I should have read more carefully. That sounds like the noise is present at that speed with the engine off and clutch in, which pretty much eliminates the engine as a possible cause. I think I'd start looking for something loose (like a heat shield or body panel) that's being tickled by wind at that speed.

honestly i dont know where to start.... i have looked around pretty well, but the main problem with that is.... it's not simply present at that speed... just coasting at speed. i can drive around within those speeds all day without a peep. it only does it at about 1% throttle and when i let up from that. other than that it does it between the aforementioned shifts.

i feel like i've looked everywhere... and still dont have a clue. :)

Keep in mind that the front of the car dives on a lifted throttle. That weight shift could affect engine position and thus everything connected to the engine, especially if the motor mounts are weak, or affect front body panels.

A "chain dragging" sort of sound makes me think of a heat shield coming in contact with the driveshaft, given that it appears that the engine has been exonerated. If that's happening you ought to be able to find rub marks somewhere.

Yes, get the car in the air and check alllllllllll heat sheilds first thing. I just had an E90 come in the other day cause they can over something and could hear an intermitent dragging noise as you describbed. It ended up being the exhaust heat sheilding rubbing on the driveshaft nearest the diff during reverse or on decel.

Another thing you consider is that it could be the exhaust vibrating on something. I've had E39 M5s vibrate on the center mount simply because someone didn't tighten the front collector bolts in a certain order, this caused the exhaust to preload in a lower position and vibrate intermitently at this mount.

And if all of this doesn't show any signs of the noise, pray for it not to be int he tranny.