Not knowing the model year it is potentially one or both gears in the rear axle differential. Sometimes called "the pumpkin" for slang (because of its appearance looking from the outside rear of the vehicle) has two gears; a ring gear and pinion gear. The ring gear typically creates the whine due to wear. Things to check for are: proper fluid level in the rear differential, also see if any metallic particles are present or contamination, such as water (been in the mud or water lately?), then check for clunking during accel and deccal. You mentioned whine during accel but try pushing the gas down and letting up (not to extreme) to see if you hear a clunk. That would indicate a bad fit up (mating) between your pinion and ring gears. The only other thing that comes to mind is the carrier bearings, which support both the ring and pinion and axles that lead to each rear wheel. They can be worn or pitted due to contamination.
U-joints typically clunk or whine only on take off (first accelerating) but w/o hearing it they could be part of the issue as well.
Good luck.
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