rebel, if it is a knock, it is most likely a stretched rod which means you will have to have the rods resized and new bearings installed.

One way to check to verify it is a rod, is to disconnect one spark plug wire at a time until you no longer hear the noise. Obviously you re-connect each wire after each try. heheheh, otherwise, most certainly the noise will disappear after about three disconnects! hahahah! Ha ha, I crack myself up!