I don’t think the clutch has anything to do with it, I’m just saying when power is applied to the drivetrain, the noise persists When power is removed, the noise goes away, regardless of speed.

The center bearing moves exactly as you describe it should in proper working order. “Bellows” is exactly what it’s like.

I jacked the rear wheels off the ground, let it in idle in 3rd, and stopped the movement of each wheel independently of the other, and the noise didn’t change. i.e., the noise was still there when both pairs of CV joints were stopped at separate times. So could it be those?

Could be the diff mounts? I’ll check.
Could a tooth of a gear have sheared off?

The sound is prominently coming from the diff. :/