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 E550 Airmatic Pump Motors May Fail Due to Sticking Relays
Mercedes-Benz E550 Problem
Average Mileage: 39,000 mi (37,000 mi - 41,000 mi)
Airmatic pump failed and was NOT covered by warranty. Also, left the suspension selector in Sport mode while the car was parked in the garage for 3 weeks which required the battery to be replaced at 28,000 miles. The MB repair service acknowledged the issue.
Visitor, 2007 Mercedes-Benz E550, 37,000 mi
The Airmatic Pump Motor was running continuously and had to be replaced due to damage. Fortunately, it was still under warranty.