Isnt it the door being open that makes the sound?? On mine there is a switch that is coved up by a rubber thing in the door jam. I took that off, unscewwred and took out the switch,a nd used electrical tape to tape the switch in the down position...A more perminant option would be to take the switch, cut the wires and tie them together, making the door always be 'closed'

Hope that helps