Loud whining noise from back of truck

[km335]

Hey guys im new to the forum my name is kyle....I have a loud whining noise coming from the back of my truck.I have a 2004 f-250 6.0 thats . Initially i thought it was the rear end but when i poped the diff cover off i didnt see anything to be wrong and the ring and pinion gears seemed to be fine. I had my buddy drive me while i i stood in the bed of the truck and it seems to be coming from where the cab and the bed meet. The sound is very loud when you are inside of the cab with the windows shut.If anyone has any ideas as to what this could be i would greatly appreciate it.
thank you

[Strokin' 6.0]

I really haven't had the time to look under my truck to see if I have a two-piece driveshaft, but my first guess would be the carrier bearing went bad, if there is one. Second guess would be u-joint.

[md18]

The carrier bearing is bolted about where the cab and bed meet. I'd say thats your problem.

[km335]

Thanks for the help guys, it was the carrier bearing.