i've been working on my buddies 53 olds 88,at highway speeds it has a slight lifter tap.the oil pressure is fine at fourty psi.we pulled the covers and everything looks fine and tight.its an oem shaft set up and it all looks good with no play.it's only got 30k on its a cream puff.just trying to figure this out.i offered him to switch to a thicker oil but he wasn't to keen on it.it doesn't have any noise at any other time and it's not an exhaust leak.thanks guys