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="" />