When driving my 2006 4wd Silverado and going 55mph or so, there is a roaring sound that has a frequency of about one second. The sound lasts about one to two seconds, stop for about one/two seconds, then repeat. When I slow down, the the roaring sound lasts longer, until around 40mph or so I don't hear it any longer. The sound is fairly faint: if I am driving on a coarse road I can barely hear it.
I rotated the tires, going on the slim chance that the tires might be causing the sound, but the frequency is just too slow for it to be the tires.
Any Ideas what might be the problem?
