My car's got a slight rattle at idle, hot or cold. It stops completely if you rev it over 1k rpm. Sounds like timing chain to me, but it's hard to pinpoint in the engine bay. You can't hear it in the car at all.
The engines got the later style chain tensioner (1 piece). But don't know if it's original or new-ish.
Having not really poked around M52's much I don't know if its normal, or necessarily concerning anyway. Cars done 118k, doesnt use any oil, and generally runs sweet