Torque tube bearings noise?
 

07 M6 exhibits a sort of whine from under the car when letting off the gas at 65-75 in 5th, sometimes in 6th. Hard to determine exactly where it's coming from, but seems like it's behind the seats underneath... the old engineer in me suspects it's possibly the rear TT bearing, doubtful it's from the diff. Only other thing potentially is 5-6 gear shaft in trans. It's been occurring for almost a year, BTW... otherwise it drives awesome...

The diff in my 07 whines on deceleration...seems to be pretty common. My halleck intake also whines under light acceleration at hwy speeds. Have found that rotating the coupler with vacuum tube helps eliminate this noise.

Had the diff checked out and was told chances a new one would sound the same.

Torque tube bearings usually sound like rocks in a can.

if the TT bearings go out at 70 mph its a wild ride....don't ask how I know