Another idea. Presumably whatever other background/chuffing sounds play without incident (for example, don't distort) when you pull the rope. I didn't realize the Sound Board had volume control...so if you turn the volume way down to just audible so as to reduce current draw through the Sound Converter, does the behavior change? My understanding is the Whistle is the most power-demanding sound in most engines - maybe this affects the AC voltage/offset in some unfriendly manner.
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