This only happens when i've got full time 4x4 engaged and i'm travelling at 40mph or above, the noise sounds like a rumbling wheel bearing but I can't feel anything though the steering, just a little harshness through the body. It only happens when on the throttle, as soon as i lift off it stops completley and it doesn't change with the amount of load or speed. I'm not too bothered as it's been like it for the 3 years and 30k i've owned the jeep but I would like an idea of what it could be. Or you can tell to shutup and stop being paranoid