Today was the first time I have heard of this type of pumping and hissing sound at the same time coming from left front tire side but I know most likly came from either the engine compartment or inside the quarter panel after I shut off the engine from a short distance trip. I originally though it was the airmatic pump, but after I tried to rise the car the car and it would rise normally and the pumping sound continuted for a couple more minutes and finally stopped.

Now I am puzzled what that sound could be? It sounded like you are pumping air into your tire from a 12v portable air pump and the hissing is like you are releasing air out of the tire, but both sound were not as loud as the actual tire air pump and the hissing was a much softer or slower.

Any idea or guess what this might be? I was so affraid whatever it was it's going to burn out..

 

No body ever heard of this type of sound before? It's very very strange because I have no heard of it since then, but I am affraid when the warranty is over this thing will resurface.. and cost me an arm and a leg.. any idea what this might be or has anyone heard of this kind of issue before?

 

Airmatic equalizing the pressures/heights.

 

How long have you had your E550?

I have an 08 E550. I hear it all the time. Its the Airmatic system.

 

I had a 500 from 11/03 to 2/07, & the 550 from 2/07 till today. They both randomly discharge or fill when started or shut down and a door is opened.