I have virtually the same car as you, so here's my advice:
1. When you put the key in the ignition, it doesn't buzz. You have to turn the key like you're going to start the car to make it buzz. To prevent this, fasten your seat belt before turning the key. It will never buzz.
2. If you shut your car off, and open the door, the car will buzz. Simply take out the key, and re-insert it, and it won't buzz.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".