Well my brother was riding my 700 over the weekend when the engine started knocking, shortly after this the oil pressure light came on and the engine died. After this the engine wouldn't even turn over. We checked the oil and discovered it was plum out. He said that in a course of 2 weeks he had to add oil twice. We let the engine cool overnight and added oil and the engine was then able to turn over and start. It starts fine but has a very loud knock in the top end that gets louder with rpm of course. What all could it be? Also we know that it isn't leaking oil so why would it of been burning oil that bad? any suggestions or answers would be greatly appreciated!