I did some testing on an isolated Fastrack oval with no accessories attached. Power was provided from the D-U posts (non-whistle control) of a Lionel postwar SW 130 watt transformer.
At first, the engine behaved the same way with the bell constantly ringing. After activating the reverse unit in the engine by moving the transformer handle to off five or six times, the bell stopped ringing and the engine worked normally.
After activating the engine's reverse unit by moving the transformer handle to off five or six more times, the bell started the constant ringing again. It continued ringing until I activated the reverse unit five or six more times, then went silent again. At this point, with a silent bell, I stopped testing.
It would appear from the testing that activating the engine's reverse unit by cutting off the power five or six times causes the bell to operate or not operate. Is there a better way to activate/deactivate the bell? Thanks.