I've got a '97 f-150 4x4, electronic shift, 63,000 miles that squeaks in the front end. Sounds like a belt squeaking, but it only happens when the 4x4 is engaged. I've been through quite a bit of mud and some water, but nothing deeper than a couple inches. Is there a seal somewhere that's out and let mud/water in? Anyone know what it could be? Thanks!