is it when you're turning? could it be a suspension problem, like a worn ball joint, that clanks a lot. or are you sure that its comming from the engine? could be a chain tensioner- those have a tendancy of staying depressed and the chain slaps against the timing cover. if you can locate a side, or spot on the engine where you hear it the loudest...that would help. Us SOHCerz gotta stay united i just picked up another one...but a dually is goin in that one.