I've got what I can only describe as a roaring noise while in 4 wheel drive. Actually sounds more like a large fan running underneath the truck. No grinding, no popping, no shaking, no rattling, just a steady roar that doesn't change with speed or RPM. Driving surface is snow. The transfer case shifts in and out of 4Hi smoothly and the front wheel drive seems to function perfectly normal. The truck does not make the noise in 2HI.

I replaced the transfer case fluid when I purchased the vehicle in October and the fluid looked old, but not burned and no metal shavings were noted. I've spent a few hours searching this forum for clues, but have not found symptoms that match mine. I have also installed the transfer case saver (clip was still intact) and have had a shop check ujoints, wheel bearings, etc with no worn parts noted. I also just got finished with a Thuren trackbar, DSS, replaced a tierod, checked balljoints and replaced sway bar links.

Probably going to take to a driveline shop as soon as I can get it in, but thought I'd post just to see if someone else might have faced this situation.

 

I took this issue to a driveline place in town (regional outfit, local shop) and have them go over the truck. They think they have isolated the noice to the passenger side front. May be a bearing starting to go, but both I and the tech jerked and pried on the tire while on the lift and could not find any slack. Guess I'll just monitor until the noise changes or gets louder.

 

Isn't there a support bearing that your inner axle shaft rides on at the point of the CAD in the passenger side axle housing that would go under leverage load while only in 4x4? Never heard of one going out but you never know..