My bike is about eight years old, and even when it was brand new, the rear brakes squeaked a little bit. Since then, I've gotten a new bike and I haven't been riding the other one. Now, I want to use the old one, but I have to get the brakes fixed first. Instead of a squeaking sound, it is now a really loud squealing sound that I'm sure can be heard from half a kilometer away. How can I fix this?