Hi Leeianne,

There are a few things this could be. The simplest, and cheapest to fix, is a stone or something stuck in the brake calliper. It'd take a mechanic five minutes to sort that out for you. However, it could be that your brake pads are worn down to the metal as well, which is more serious. Either way, the sooner you get the wheel off for someone to look at it the better.

Hope that helps.