+1. there really is no way of knowing for sure weither it would be rod knock. you would be able to here it. its like beating a spoon on a cooking pan. also, check your timing chain. if you put your ear up to the valve cover, and you can tell that the noise is coming from the head and not the bottom end, then its not rod knock. but like punisher said, it could be valve tap. check for a stuck lifter.