Mine have always made lots of noise at highway speed. Extra case = more gears spinning and more noise. Did you check your gear oil? Low gear oil could also create more noise.
Oil level is fine. Does yours sound like mine? From what I've read, it does make more noise...I just wanted to know if its the same as mine. If it does, then I won't have to tear it apart anytime soon just to find out there is nothing wrong with it.