In early DCC days..
This could be F2 set to toggle, rather than momentary. - But would depend on which function the bell is activated by?
I would think the reed-switch, or its wiring could be trapped / shorted somewhere. - A three-wire lead, running from the board in the motor-block, to the circuit board.
If you are lucky, two black, one brown wire (for identification).
If not, three black, and you might have to investigate a little harder.
PhilP