I don't know if this has been brought up before, but the last time I went to Tom Sawyer Island, I was admiring the inner workings of Harper's Mill. While watching the gears turn, I noticed the groaning noises of the mill and as I listened, I realized that the mill "sings" Down by the Old Mill Stream. I've never heard anyone mention this before, and wondered how many out there have discovered this "hidden" effect. Next time you're on the island, stop by the inside of the mill and listen. It's a very subtle effect, but really neat.