We have a Nutone Scovill Intercom 3003 series which has a buzzing noise in the speakers.The radio still plays and the room to room intercom still works,however the outdoor to indoor system does not work,and their is that buzzing sound.Its gone out once before,completly and the service man said that it was lightning related and replaced a printed circuit board.I watched him replace the circuit board and it looked fairly easy,I could probably do it myself if I had the part. Any help ?