Strange noise coming from the rear

[Ken92SVX]

Hi all,
I posted a tread early about a high pitch whining noise while driving. I finally had some time to do some further trouble-shooting. I checked underneath the car and did not find any vibration related causes.
I then rotated tires- no change in noise.
Put in FWD fuse and noise went away.

For now I am pretty convinced the noise is coming from somewhere in the drive train. I had also changed the fluid in the rear differential and checked the plug. I found no evidence of gear damage there.
I also pushed and pulled on the drive shaft all the way back and everything seem to be OK from what I thought.
The strange noise appears to change pitch/frequency when driving the faster I go the higher the frequency.
It is throttle related- if I let of the gas, it changes briefly, and then it comes back.
Any thoughts as to what in the rear/drive train that could cause the noise?