I have a 2001 Audi a4 1.8t quattro manual. I have a relatively loud knocking sound. It only comes after the car has come to the normal ideling point. If I rev to 2500 quickly I can try and make it come back. It's a knock, not a ticking or anything else. My stethoscope here's the noise from mainly the front but I can hear it all over. I don't think its the cam chain tensioner for that would only come at cold starts when oil hasn't been circulated through the engine, not after its at normal idling level. Here's the catch, when the knock comes it stays for a little then leaves, I don't hear it at all when the cars moving. If I take the serpentine belt tensioner and take just a tiny bit of tension off, then the noise is gone. Even when I rev. I've replaced most of the pulleys in my car trying to track it down. Anyone hear of this before? Thanks for your input, any advise helps.