okay, I saw this thing at a nearby haunted house and I want to build one for my interactive mad science lab.

It was a black dome (half-sphere) about 20" in diameter, and when you touched it, it made noise. Kind of a squelch sound, like you were turning the dial of the radio but not finding any stations. (also kind of reminded me of the sounds my dad's metal detector makes)

Does anyone know what this device is called, or where I can buy one or learn how to make one?