fluttering sound from center/rear of car off throttle

[Torque]

When it gets hot (after driving 15 or so miles), and I let off the gas to coast, or start to brake, the car emits this strange fluttery sound from the center or rear of car (think zip tie in bycicle wheel) ... and it speeds up in its cycle the faster I slow down (more fluttering if I'm jamming the brake as opposed to coasting to a stop). Does it with the clutch in or out, regardless. I don't really even know where to start since it only does it hot.

When I apply throttle it goes away.

Help.

Car is a 6/89 (MY90) 535im w/ 141k on the clock.

[Morgenster]

Does it happen in reverse?

[Ross]

This one's a first.
My first suspicion is something with the driveshaft, the center bearing perhaps is moving around.
Does it sound like something is actually making contact with rotating parts?
Exhaust or shield hit by the driveshaft??
Please keep us posted.

[Torque]

Well what's even worse, it wont do it on every drive ... I just went and drove around and not a damn thing.

And yes, it definitely sounds like a dull metal sound (like a heat shiled or something), but I've looked and I can't see anything that could do that.

I'm gonna be putting it on a lift Friday to do front brakes and fix one of the fuel tank straps so I'll see if I can duplicate it while "driving it" on the lift.

[Torque]

Alright guys, it's all fixed. The very end of the heatshield was scraping the driveshaft (and polished a 5cm section of it quite nicely, i might add). bent that out of the way; all is well.

Was quite easy to find once the car was on the lift ... since the driveshaft/diff moves down with no load it started scraping as soon as i started letting the clutch out on the lift.

whew. at least it wasnt something worse