a worn our chain itself does not make any noise.It is when the tensioner is no longer keeping proper tension on the chain that the chain will slap and make noise.One reason that the tensioner not working proper,internal ooil leack and the tensioner is only using its spring to keep tension instead of ooil preasure.Another is when a chain is very badly worn and the tensioner is reaching its max point.And at that point you are in trouble.Another if someone is neglecting on the oil changes ,or low oil level