Idea 3 was bounced around on this forum several months back. Wasn't my idea, but I do endorse it.
The premise, IIRC, was to use near-field communications to sync up with "beacons" that would give location info to the throttle to let it know what sounds to emit. (nearby business sounds, construction equipment, vehicles, wildlife, adjacent trains, etc.) And of course, *your* train would be in the mix as well.
