How about if you pop it into neutral as soon as you let off the gas? If it is there then it is the side wheel bearings in rear axle. if not then it is the pinion bearings.There seems to be a whine from the rear end
It is not present when the car is under power, but is present when I lift off the gas and the car is coasting.
U Joints checked out fine.Pinion bearing or pinion support bearing loose allowing the pinion to "shuck" when contacting the "coast" side of the teeth.