m20 unknown noise - video

[RCM3]

http://youtu.be/17dGiA3ff9M

The noise started yesterday, after I let off the throttle, right when engine RPMs begin to fall. Its hard to describe, but its that whirring, bearing-like noise heard behind the engine noise. It mainly occurs at high RPMs, above 5k. I am stumped at the moment, the car still runs great, no noise at low RPM or idle. The noise is also there at every downshift and when in neutral and the engine is revved but ONLY when the car is rolling down the street. If I were to try and replicate the noise in the driveway with the car stationary, I hear nothing abnormal. Thanks for the advice so far guys.
Car: 1988 325is


-Ryan

[!kid]

possibly drivetrain related not engine related.

[gt88]

check your exhaust hangers, and your trans/motor mounts- as you said "must be moving"-
good luck!

[efficient]

i like the way your car sounds.

[RCM3]

Thanks for the help guys. I discovered the issue. I must have bottomed my exhaust out which caused a separation where the exhaust is bolted together after the cat. One side had enough play to allow the ring that is seated in the joint where the two exhaust pipes meet to rattle around and cause that strange noise.
Thanks again!