i'm getting a knocking sound coming from the #4 cylinder. i checked the spark plug boot and there was brown stuff all on it. i'm thinking its that my valve is knocking with my piston. it was weird because, it started happening after i rotated my wheels. so, i originally thought it was something to do with the wheel weights or something of that nature, but then today i realised that this is what happen. how can i fix it, and what will happen if i drive too much on it?