You sure this noise is coming from the frontend?
Any vibration in the truck?
Not a transmission or transfer case? Some times not always: have seen bearings in the shaft coming out/ though the transfer makes a roar like sound. Just before the shift forks between low/high went bad. but you are saying the front and this is under your seat.

 

Im beginning to think it is something o do with the transfer case
I am looking into that