the door alarm switch is located near the key. As it close when the key is inserted, you just have to open the circuit permanently, by cutting and insulating one of the wire at pins 3 & 4 of the connector.
What i've done was - i disconnected the neg- wire connector inside the door switch. Very irritating sound gone but at a cost: the car will not know if door is open or closed. Careful not to leave your keys lying in the car as the auto-lock will activate.
Remove one phillips screw, pull the door switch out, disconnect the quick connection. I taped mine to the switch so i wouldn't lose the wire and connector. replace the switch and don't forget your keys!!!