Bearing hub?

Put the truck on a rack, check the rear end fluid. You should be able to touch it with your little finger in the hole. After you get some fluid on your finger rub that finger and another together see if there is any gritty feeling, the rear diferental fluid lubricates the bearings. If the fluid is low add correct differntal fluid, the rear bearing could be going bad.

I had the same problem. Seems the axle wasn't heat treated right. The race from the bearing wore the axle. I had to replace it. Mine started to vibrate after the grinding noise started

After checking the lub and finding no metal shavings we changed over to bgls2 additive with the thought that this would clean the "clutches". It worked, no need to r&r seals.

Keep an eye on the drive shaft, my wife has a 2003 and the driveshaft was enclosed, what we found was that it had never been lubed when put together. She had rear end noises and they ended up replacing the whole rear end along with the drivshaft.