bearings will make noise at 30- 40- 50, etc MPH. If the noise comes on at 55-60 mph, see if it goes away at 70-75 MPH. It could be gear whine. Changing the rear end oil charactoristics can help. I keep 75-w140 in it and added friction modifier. That helps. I also run it 1/2 inch overfull, that can help. Possibly a different oil would help. 80-90 seems to be worse for noise. Full synthetic seems to help ?? JUst my experience. Make sure the alxe is FULL... add a cup and see if that helps.