it has a 5.3 with auto lock posi rear—sounds like a combination of tire whine and bad wheel bearings–the faster you go the louder it gets—and it all goes away when in neutral–even if rpm’s are kept constant
Sounds like a bad carrier bearing in the differential.
I shlould have also stated the unique vibration that occurs when at speed–in the float area between accel and decel—sounds almost like a jake brake and vibrates bad
It could be a bad pinion gear shaft bearing. If the pinion gear shaft bearings have lost preload and are loose due to the bad bearing it could allow the drive shaft to wobble in ‘float’.
You might block the front wheels; shift the transmission to neutral; and try to move the differential end of the drive shaft up, down, and side to side. If there is any looseness, you have zeroed in on your problem. You might get by with replacing the crush sleeve and resetting the preload but the noise indicates you will probably need to replace a bearing. Hopefully, it is the bearing that comes out when the companion yoke is removed to replace the crush sleeve.
Hope this helps.
any place to start is a help–everyone I talk to thinks I’m nuts, and most said it was the torque converter. On another note after driving another car for a week and then driving my truck again–I noticed a high speed vibration when I started the truck and the only thin I can think of is the harmonic balancer–thoughts?