Just bought a 1996 BMW M3 w/ 135,000K miles & a manual trans. No mods have been made to the engine. I have noticed a sound at idle that sounds like the pistons knocking or the valves tapping. It is not extremely loud, but it is noticeable. The frequency of the tapping increases with engine speed. I have heard about issues with the chain tensioner, and also about how some BMWs simply have a 'diesel knocking' sound to them naturally. What do you think this knocking could be?
Thanks, Niles