I'm new to the forum but I have a wierd problem. I have a 1999.5 a4 quattro, on cold to semi-cold acceleration I get a sound from the right side of the engine compartment that sounds like a valve nocking, but is loud enough to be a exhaust problem. The problem only happens under acceleration. It sounds kind of like a space car from the jetsons. Does anyone have any clue what this might be?