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 S430 4MATIC Airmatic Pump Motors May Fail Due to Sticking Relays
Mercedes-Benz S430 4MATIC Problem
Average Mileage: 74,500 mi (54,000 mi - 94,000 mi)
Visitor, 2003 Mercedes-Benz S430 4MATIC, 54,000 mi
had mecurly mercedes put in new pump
it keeps hissing, just want to know possible solution.