Hi all, I recently bought a 2012 A4 quattro wagon and I'm having a rattling noise coming from the engine. My mechanic says he can't said he can't tell where it's coming from. I checked the heat shields and they are fine. My check engine came on after I bought, took it to the dealer and they replaced the diverter valve, which fixed the light but I still have a rattling noise coming from the engine bay. It sounds like a bicycle when your not pedaling when the engine decelerates. Any insight or advice is greatly appreciated