Kieth does make a good point. I just took you on your word about the knock. Hmmm what else could it be? It would definitely always be there and not go away…so again Keith got it right. If it sounds like a sort of “loose” sound or rather like chattering…that would be your Timing chain being stretched beyond the adjust limit of the Hydraulic Chain tensioner…Did it sound chattery? If so I would second the chain idea…not that serious…or I mean that can be repaired and nowhere near as bad as a Rod Knock at all.