I have been looking thru the threads, trying to find an answer to a tapping noise. You guys seem to now your stuff! My hubby is pretty sure it is not a valve. Engine makes a tapping sound, only in gear, hot or cold. I saw one poster had trouble with a Mott valve. I am going to tell him about that. Any other suggestions? I did take it to a German cars only mechanic, he's baffled. Not good. It is a '04 C320 Sedan.