That sound that you refer to as a bell may not be a bell at all. I remember riding those years ago, and just after the conductor closed the door, he pushed a button that made a buzzing sound just like you hear here. That, I believe was supposed to warn station platform people that the train would be moving shortly and to stand back. It also served as an audible signal to the train engineer that all doors were closed and it was safe to depart. I vaguely also seem to remember that the buzzer was pushed just before the doors were opened at a station stop.
I do not remember ever hearing a bell from any post-1960 CTA EL car.
Chuck
