I have a humming at 3100 - 3400 rpm in 3rd 4th and 5 gear. It will go away if I accelerate. Or if I decell but if I decell through it like 3800 down to 2800 it will come in at 3400 and go away at 3100. It is a loud whining and humming type sound. Mods are as follows Stock clutch 3" down pipe and 3" exhaust stock cat. Intake, AFC,and boost.
The sound was there before the 3" downpipe was put on also. If it is the tcase then I will take it in.

 

Sounds just like mine when my t case decided to die. If it is hope it goes well at the dealer.

 

I get a whine when I decel while in gear through mid RPMs. Seems to go away at lower RPMs. I figured it was just driver terrain noise. Oh and my car is completly stock.

 

I get this too. I have had a bad transfer case but this sound is not nearly as bad. I'm not worrying about it at the moment.