rear end whine

[tate]

Hello all i have a 2000 tahoe with the G80 rear end. since i bought it used it always had a light whine around 55mph that only happened while maintaining speed ..under accel it died out and if you let off the throttle it died out. Recently changed the diff oil with a 75w90 synthetic as recommended and the whining seems worse. it is not a growl but a more high pitched whine. i had a local shop listen and he said he would drive it as it doesnt concern him unless its a growl and he ruled out the pinion bearing. Just wondering if anyone else in here has had this problem.