Hi guys, My 05 yukon xl has developed a low humming noise when keeping a constant speed between 32-38 mph. It may be there above that speed But, I can not hear it due to road noise. It is not all that loud. My wife can not ever hear it. It stops when I take my foot off of the gas. I can hear it better with the windows all up. I have tried driving down alleys with the windows down hoping that the sound would bounce off of the buildings and I could pinpoint it. No luck! The best that I can describe it is the exhaust drone sound that I had on the freeway in the 95 silverado with flowmasters. I checked and greased the u-joints. They are fine. It sounds like it is coming from the rear or center of the truck. Here is more info: Front diff is 10 months old, out of a truck with 30k miles on it. T-case is 5 months old. Straight from GM. I checked the fluid today and it looked pretty darn dirty. Which is a surprise to me as I only run 4x4 every other week down a dirt road to "exercise the system" and keep everything lubed. I had a backing plate rubbing on my rear brakes. So, I pulled them apart today. I noticed when turning the axle shaft it was like I could feel the teeth meshing in the rear end. (The rear end fluid is about 2 months old and I used AMSOIL, the level is still good.) Either that or a bad axle shaft bearing. I think that I notice the noise when going into a sweeping curve to the left more than the right. I have never felt the teeth meshing on a rearend like this before. Is that normal? Would a bad axle shaft bearing stop making noise when I let my foot off of the gas? I had a pinion bearing go bad on my 03, it was a high pitched noise but it stopped when my foot came off of the gas. The sound from that traveled up the body and sounded like it was coming from the front. Any recommendations would be very much appreciated. I have done a few rearends. But, I am voluntarily ignorant when it comes to them. Sorry for the long post. I am trying to give as much info as I can. Thanks!