I have an MTH 20-2040 Southern Pacific GP-9 engine, pictured below. I operate the engine conventionally on an isolated loop of tubular track, using a Lionel prewar type V 150 watt transformer. Except for the initial reset state, the bell rings constantly when the engine is under power. No instructions came with the engine, and I am not very familiar with MTH products. Is there a way to turn the bell off? Thanks.