No specific circumstance. And it doesn't happen all the time. But some times stopped at a light... in drive... I hear a "dunk dunk dunk" from the rear of the car. Hard to tell... but I assume there isn't too many components back there. Anyone have a similar situation? I was thinking fuel pump. Thoughts?

Helpers!

I haven't heard anything like that on my w203, but the wife's '04 Audi TT makes a popping noise at startup. Apparently it's the OBD II system testing the evaporative control system integrity. I think it pulls a vacuum on the fuel tank air space, as the noise sounds like a pop-off relief valve to me. She tried to get confirmation from the dealer, but nobody there claimed to know about it.