Originally Posted by Volvo Diesel

I would be very interested in hearing what your dealer has to say about the noise you are experiencing, as my wife's E350 wagon makes the same noise. I notice it more on cold starts and occasionally when starting the car after it has been driven and then shut down for more than 30 minutes.

The service advisor at the MB place here said not to worry about it, but it is not a pleasant sound, even though it doesn't last long.

There is a post or two on BenzWorld about this, but no one has reported back with a resolution to the issue, except one reply which states that replacing the "air pump" made the sound go away????

Good luck.