Anyone know what would happen if you run a humidifier with no water?

I'd be cautious. Even the cool mist ones have a heat coil (or something similar) in them. It could be a fire hazard. We run ours dry, but it's only out of water for a short time. And be sure to clean these things 'cause YUCK! :) I'd try the white noise machine. We even travel with ours. :D:D It is our lifesaver! Kelley