getting slight winning noise in cruse, stops in coast. on 2001 GMC Sierra 2500 HD

rear end winning noise in cruse, noise stops when in coast. Oil just replaced at 70k no metal found. also what is a good repair manuel?
Thanks Jack

Asked by for the 2001 GMC Sierra 2500 HD
Chilton makes a good manual. Hope your differential has been fixed by now. But if not most likely the pinion bearing is bad.