The following was posted by Thomas Kaminski.
I just repeated Alan’s experiment with a 4″ by 3″ (roughly) sheet of aluminum foil and tap water. I placed 250 ml of tap water into the talk of the VivReal ultrasonic cleaner. With no aluminum present, I observed the “snakes” that Alan saw, mostly in the middle of the tank. The first run was for 120 seconds. I then exposed it for another 900 or so seconds leaving mostly aluminum dust.
During the run, I did observe small bubbles forming on the aluminum surface and floating to the surface of the water. They often persisted for a while, then “popped”.