T56 Chirping sound, maybe something else.

Greetings,
06 CTS-V 114k miles.
I'm not even sure this is a transmission issue but, I'm throwing money at this thing. Just had the rear diff rebuilt because, well it needed it. I thought this noise was a pinion bearing issue (it was bad), replace axles while I was in there, carrier bearing is new, replaced with the voodoo chicken product, shifter is creative steel product. So, after the diff rebuilt, I was sure this noise was related to the diff as the diffs are the weak point in these cars. However this weird noise is still there.
It appears after the car had been on the highway for awhile, in other words very warmed up. It appears on decel thru about 70 to 60 MPH. I doesn't matter if its in gear out of gear, clutch in or out, in neutral etc. It's a squealing noise, like a chirping sound. Still has the factory original clutch, pressure plate etc.
Car shifts fine I'm just getting this chirping sound under these perimeters. Wheel bearings seem fine, no rubs on the propeller shaft, its just frustrating because I can't pinpoint it.
Thanks in advance.