A buddy of mine owns a 01 7.3 4X4 and he has some serious drone noise going on. It seems to occur when accelerating and decelerating, then there is stress on the drive train and between about 45 and 65mph.
I'm thinking it could be carrier bearing, what do you guys think?

 

I had something like this happen to me. Tell him to make sure his exhaust pipe is not touching metal somewhere down the line. My down pipe was touching the firewall and the drone was sooooo bad.