define knocking, we talking a repetitive knock that increases in rapidity when the throtle is depressed (that would be end shells at a guess)
or just occasionaly and only once or twice (slight miss, or late ignition, this will be solved with a service)
just over bumps u have a knock from the engine bay(something in the running gear but probly bushes)
the only one to worry about is the mains being shot, that said they are a piece of p**s to swap out on a 2i and cheap as hell