Way back when I was a motorman in the Cambridge Subway (now the Red Line). I was doing the last westbound train to Harvard and we used to stop at Washington and Park St. stations to meet with the other last trains on the Main Line and Tremont Street Tunnel. I was sitting in my cab one night and i heard a train whistle and thought I was hearing things. Then I heard it again but just a little different tone. So I got out of my cab and there was a guy sitting on a bench with a whistle like device and he had an audience. His hobby was traveling around the country and recording train whistles on different railroads and then making these whistle things to imitate them. He could even duplicate our whistles.