Transmission or Rear Diff?

This whine has gotten progressively worse over the last couple weeks. It is definitely coming from the mid to rear. At first i thought maybe it was an exhaust whine. Like something humming. But now I've accepted that its something more critical. Highway speed and the whine is very distinct when pressing the accelerator. It quiets down when I let off and coast but does not go away completely. Is their someone way I can narrow it down to either trans or diff (maybe a rear bearing??). I do not mind doing what is correct to extend the life of this vehicle (250k and runs like a top) I just don't want to start blindly replacing expensive components if i don't have to.

In the video you can hear that I am pressing down and then letting off the accelerator. The whine is distinct when accelerating
2001 GMC Yukon XL-1500 2x4 automatic 4L60E

Tranny bushing/bearing or Rear Diff/Axle bearing. Typically its one of the axle bearings but easily can be a Diff support bearing or pinion bearing. Gonna have to get it on a lift and find out.