2001 chev 1500 rear end

Check to see if your outter wheel bearings are loose, to do this jack up the rear of the truck about 2 inches away from the ground and push and pull on the wheel. does it have any play? if so you may need a bearing and race or cup for that wheel also try wiggling the tire back and forth to see if there is any movement. If there is none check oil level is it full? yes? then strut truck up put it in gear and see if you here the whine. at what speed is the whine? Or if it went away while running off the ground then you have a tire problem if you need more help post here for the rest of the story.