Starting just two day ago, and happening 3 times since then, I've had a loud chattering coming from the engine. The best I can describe it is like a bad throw-out bearing, but is an auto. It happened once after a 30 minute drive, and I let it go. It came back when I got back in the car, but once the tranny shifted into 2nd gear above 2K rpm's it went away and didn't come back until tonight. Again, it was there after the same 30 minute drive I take all the time. SO after coming into work for an hour, I started the car and heard the chattering. popped the hood but couldn't pinpoint it. Sounded like ti was coming from the front of the engine, and I could almost "feel" the vibration. So then I made a slow circle around the parking lot to see if it RPM-dependant, and it is. So I parked it, and revved the engine slowly. I wasnt'watching the tach, but somewhere around 2 grand or higher it went away. Turned the car off then on again, and it was gone.
Any idea what this might be?
The car is an '04 A6 2.7T with 66,575 miles.
A mechanic I spoke to in the fall said when water pumps are getting ready to fail, they'll occasionally make a chattering noise that people usually ignore.
Could that be this, if it's intermittent and disappears with a blip of the throttle?
I watch the guages vigillantly, and the temps are all fine, and no CEL's.
Any help is appreciated,
Thanks,
Jeremy

 

Sounds more like a camshaft adjuster to me. You really need to get a stethoscope to help pinpoint the area its coming from.