Did a gig with multiple stages. The overall theme was "railway" (Railfair 99). One of our stages was located next to the main spur track that was used to move engines about the event...One day, we were in the middle of "Rolling Home"... we've tweaked it a bit, with a retard with harmony at the end. We were right in the midst of an acapella bit when the ol' 4449 (one of the largest engines there) rolled by and blasted a friendly shout out of it's whistle. After the 10-15 second blast, when we could finally hear ourselves again, we were all in different notes, keys and states of pain. After that show, we all resolved "no more harmony on THAT STAGE!"
M