2008 f450

I have a 2008 Ford F450. The rear had been rebuilt 4 times and going on #5. There is a whine at 40 mph and they keep replacing the bearings. The truck has 30,000 miles. I do not tow or abuse the vehicle. Has anyone else have this problem? The Ford rep will finally be here to help in this issue. I have requested that the whole rear be replaced. I think it may be in the housing or punkin.