Low humming noise when keeping constant speed, 05 yukon xl

Discussion in 'GM Powertrain' started by Pikey, Sep 4, 2013.

  1. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    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!
    Last edited: Sep 4, 2013
  2. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner 1000 Posts

    I hate tracking those mystery noises. Looks like a lot of stuff is newer. I would figure bearings to whine at more speeds. I had a similar one, one of the times I replaced my output shaft seal. At start I would get a high pitch squeal let off gas and back on and it would go away. only at low speeds, but started right after the change. Ended up being the boot was rubbing just right on the drive shaft. A tiny bit of grease and it didn't do it any more (which is how I figured it out). ended up replacing the seal with the OEM one which was much better quality. Wish I could be more help
  3. zippstripp

    zippstripp Member 1 Year

    Sounds like tell tale sign of a pinion bearing to me. When the fluid got changed in the rear diff. was there metallic(silver like) streaks in it? If so further inspection would be a good idea.
  4. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    Nope, no metal at all. Really nothing on the magnet either. I had to drop the cover to change the fluid so I checked everything well. Today was interesting. We had to go to an open house at my son's school. So, my mom watched the kids while me wife and I went. I had her drive the truck while I crawled all over the inside with me ear against the floor. I really heard nothing by the rear axle. I did have some noise by the rear of the trans. So, tomorrow I will throw new ujoints in it. They are cheap. Maybe it will fix it, maybe not.
  5. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    You dont have a carrier bearing on the rear shaft do you?
    I had 2 early 2000's model trucks have similiar problems that ended up being carrier bearings, one had bad bearings and the other had bad rubber supporting the bearing.
  6. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    Nope! Straight shaft.

    - - - Updated - - -

    I stopped by the rear end shop today. He said that he hears a little noise. But, not to worry about it. It could be another 100,000 before it develops into an issue. Just keep my ear on it. He knows how I am with my truck, so if it starts getting louder I will make a return trip.
  7. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    Update: I took the truck to the trans shop that installed my transfer case. They drove it and said that they heard the noise also. Checked out the transfer case and it is fine. I was getting really tired of listening to it. So, I jacked up the rear end and put some jackstands under it. I set my parking brake all the way to the floor. Then I hit the gas. I could hear the noise when the speedo read 30 mph, but I could not pinpoint the sound. I waited till my wife got home, had her hit the gas while I was under it. I found that the noise was coming from the muffler. The heat shield that is welded to the top was resonating only under load at certain rpms. But, if I left the truck on the ground and break torqued it the noise would not happen. I grabbed a pry bar and did a little "custom" work to the heat shield and the sound seems to be gone. It was odd to me because every heat shield noise I have heard has been a tinny sounding rattle. This was a low hum.
  8. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner 1000 Posts

    Good job on the detective work. :great: Glad it ended up being something simple

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