1997 Ford Explorer Whining Noise

U joints tend to give a squeaking, not a whine, your description is of a bearing nature, eithe at the wheel, or inside the rear end, and with you description, could be a carrier bearing, or pinion bearing, though carriers get quiet in coast, pinions dont. Any oil leak at the point the driveshaft attaches to the pinion yolk? If yes, it's a teltale sign the pinion needs work.
I havent heard that Ford rear ends cant be repaird, I have done a few without any problem.