So got a question for those more knowlegable than me. I've got a horrible noise coming from the underside of my truck. It sounds like a loose rattling that only happenes when the truck is in motion and I'm on the gas. When I'm stopped and reving it, nothing. I've decided that it has to be the 4x4 (possibly transfer case) because it will stop when I switch over into 4 wheel high. Could I just be that I need to top up fluids? I'm honestly stumped here because I've never encountered this before on any of my other trucks.

Thanks for y'alls help...

 

Have the IWE's checked. They are your front hubs. Default position is locked, and when in 2wd, they are unlocked by vacuum. If for whatever reason, they do not unlock, they make a grinding noise, that would go away when in 4x4.