I had a squealling noise coming from f.o.s wheel and that turned out to be the wheel bearings. Mine where totally shot, and I mean in quite a few pieces. The seal had gone and I had no sign of wear until one day the wheel just locked up! Best thing to do is jack it up and hold the top and bottom of the wheel and shake it, it should hardly move, if any movement at all. If its more than a tiny amount then is probably bearings.