Sounds like the wear indicators on your brake pads. The ones on my Monty have a metal strip attached, which rubs on the rotor when the pads have worn down to their minimum thickness - this makes a high-pitched metal-on-metal squeal (<img src="/forums/images/graemlins/oink.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" />).

Cheers <img src="/forums/images/graemlins/smile.gif" alt="" />