[folivier]

On my '98 I couldn't hear an air leak until I bought an air leak detector. I put it in each basement compartment until I found the culprit. There was a coiled up section of 1/4" tubing with a nipple and plug in the end. The plug was leaking, cleaned up the threads, put some new teflon tape on it, tightened it and no more leaks. Not sure what the tubing was for since it was just coiled up and stuck in the bundle of wires up in the middle. So your leak could be anything from factory to a previous owner.