So, I maintain my girlfriends Cherokee. It hasn't needed anything but new fluids as of yet, so things have been simple. (1999, auto, 50k miles (she got it at 40K), typical white with no mods., a bit of off roading but nothing crazy)

But now...there seems to be an issue. The truck gets loud at speeds over say 60mph. I guess that is fairly typical, except that this thing gets too loud AND importantly the sound has a wave pattern to it. The pitch (which is low) goes up and down, in a 15 second wavelength. The truck drives fine and there is no evidence of this at slow speeds. It doesn't matter what kind of driving surface (as long as the surface isn't so loud so as to drown out the truck noise) this wave pattern appears. I recently changed the auto tranny fluid and filter and all went well. Could I have fit the filter incorrectly or something (please tell me no). I will rotate the tires for the first time today(10K old Bridgestone Dueler AT Revo). Thansk all <img src="/forums/images/graemlins/kewl.gif" alt="" />

is there any vibrations accompaning the sound? have you check the rear end fluid? have you checked trany fluid level? sounds like it could be tires or a bearing.

There does seem to be a vibration associated with the sound but it is very subtle. I can feel it in the arm rest. The tranny fluid level seems good although it find it hard to get a consistent reading (I drive a bit and then check it at idle). I do want to change out the rear diff fluid. I have never checked it. There don't appear to any leaks..unless its been dry since she got it. The noise is relatively new.

I just rotated the tires. I took a short ride and got some noise at 70mph but it didn't seem to vary like I described before. I may not have driven it long enough though. My girl will be taking an hour drive today, so I will get a report from her. A wheel bearing noise would change with turning? And be noticable at lower speeds? Thanks for the input.

i was thinking about the pinion bearing. it will be more noticable at high speed and the sound goes in and out of phase with the tire noise. for a quick check go under the car and push and pull really hard on the drive shafts with the jeep in nutral and the parking brake set. there should be NO movement, and you should eb able to do pull ups on them. if it does move find the source of the movement. roll the shaft back and forth (it will let you a little) the caps on the u joint should only rotate, if you see them move up or down or in and out its a bad joint.

Howdy John
I use those tires too. Mine have begun to howl the same as you describe. One of my trucks wore the front tires abnormaly and made a bunch of noise when we rotated them the noise moved to the rear and got a bit quieter. My personal truck just keeps getting louder as I put more miles on those revo's. Roll your window down and drive slow and listen as you stop. Then srart off and listen as you go to hiway speed. Mine gets better the faster I drive.
I really like everything about these revo's except the
noise. Of course it might be something else. Wheel bearing or rear bearing... But when you mentioned revo I thought I'd chime in.
Big Jim