Both of my trucks do it at about 120kmh or 80 mph. I know a few other guys that have the the same noise. I think its because our trucks don't have hubs and the driveline and frontend parts rotate all the time.

 

Check to see if any of your PS hoses are rubbing on anything, or if the big "C" weight that is on them is hitting anything or is noy tight... My 12 started doing that and I turned the weight just a hair, and the humming/vibration stopped...

 

Thanks Megaramasaur, I will look into that today. I think that this is more than a normal hum though. It started out as something that I was able to ignore but has gotten louder and louder within about 1000 km. When driving with the music off, it is much louder than the engine revving. What does it sound like when a front diff or tcase is going?

 

I had this same problem and it ended up being the rear diff pinion bearing. It would do it at about 40+ mph and I could feel it in the floor. They went through the frt diff, transfer case, wheel bearings, etc. Eventually they took the rear driveshaft out and the noise was gone. Good luck and i hope this helps

 

Check your u joints and your carrier bearing while ur at it..

 

Yesterday I checked the PS hoses and front diff and everything looked fine. The front diff was in good shape and I figured it could use some new oil anyways. Would you be able to feel any play in the pinion bearings? I appreciate the advise.

 

Mine had the same issue. Only heard it when I would hit the accelerator between 35-55mph and would go away when I would take my foot off the gas pedal. Thought maybe was a tranny issue at first, but just couldn't pinpoint where the sound was coming from.. Found a vibration on my column shifter...found I had a transmission cooler line had come off its hangar and was vibrating causing the whining. Didn't cause any damage...just re-hung the line and the whining was amazingly gone. Hope this helps.

 

I decided to take the truck to the dealer and they found that the sound was coming from the rear diff (bearings on both axles were worn out) and from the front u-joint on the rear drive shaft. The truck only has 155000 km so I'm a bit surprised that it has worn out bearings in the diff.