"harmonics" noise

This is just a guess, but I'm thinking the drive line pinion angles are wrong. The reason I think this is the problem was present when the rig was new. You can replace the carrier bearings, but if the angles are not adjusted correctly the problem will still be present. Use a digital angle gauge, and using the lip of the transmission pan as a baseline, take a reading and write that down. Then take a digital reading in the middle of the first driveshaft. That reading should be 1.15 degrees lower than the trans pan edge. The second driveshaft should be 3 degrees, and the fourth 4 degrees. This is on my rig, but your rig may vary. The way to adjust the angles is by putting 1/4 inch plates under the yokes which lower or raise it depending on your needs. If the yoke at the differential needs raised that is done with a shim under the springs. Drive angles must be more than 1/2 degree and less than 3 degrees from each other. People who can provide this hardware are L&W Engineering at 574-825-5351. A two driveshaft setup would be different but the same principles apply. It would be good to consult a professional drive line shop. Camping World and regular mechanics will not solve that kind of problem. A simple and easy way to rule out this problem is to jack the back end up, put it on strong jackstands(on concrete), and run it up to 55-60 mph and have someone observe the driveline for vibration.