the buzzer should be behind the cluater. pull the gauge cluster, and get the car to make th buzz. feel around at the little boxes with wires going into them attached inside the dash area behind where the cluster was. when you find the buzzing one, I would think it would be easy to disconnect.
If you are talking when you turn the key, and the doors are closed, that buzzer, not sure. but the door open and key in the on position, the door pin is what activates it. and I am sure one of the wires tot he door pin switch is wired to turn ont he buzzer.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.