The relay which turns the airmatic suspension pump on may fail causing the pump to run continuously. This can result in failure of the pump motor or a dead battery as the pump motor will continue to run after the car is turned off. Also, Worn airmatic pump mount bushings can causes noises in the front axle while driving on bumpy roads or a buzzing noise while the pump is running.Google+
Car Problem Reports
Mercedes-Benz E350 4MATIC Airmatic Pump Motors May Fail Due to Sticking Relays
Mercedes-Benz E350 4MATIC Problem
Visitor, 2008 Mercedes-Benz E350 4MATIC, 55,000 mi
After a week in LT airport parking, I returned to a pimped out wagon. The air had released from airmatic but fortunately, it filled back up after a few min of engine idle. Still, dealer is replacing under ext warranty. Also, I gather this is a June 2012 recall item.