Rear Differential on 2001 Ford Expedition

There is a whining noise coming from the back side of my 2001 Ford Expedition. It's more apparent when I accelerate the vehicle down the interstate. However, when I release the accelerator the noise lessens. I was told this could be the rear differential. Is this true and how much would something like this cost??

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1 answer
bearings bad in rear. about an 800-1000 repair.

Roy