my friend was driving his car all of a sudden getting of the express way he heard the engine starting to make a laud rattling noise, it never overheated and it still ran, I followed him home another friend opened up the front valve cover and there seems to be a lot of play in a couple of the Rocker arms one even seems broken, my question is does this sound like it could be the cause or is it part of a bigger problem and how are the rocker arms replaced without pulling the engine completely apart????????????????