Today when i left school there was a slight scraping sound coming from my left wheel when i got home it was screaching. Inside there was grease all over the back of the wheel and on the brake. I am not sure what the problem is and the whell was smoking. I think that it is either the wheel bearing thats broken or the brake pad has worn too much. or possibly the some sort of axle problem. please give me any ideas of what the problem coulde be