Singing Tesla Coil
"This is a solid-state Tesla coil. The primary runs at its resonant frequency in the 41 KHz range, and is modulated from the control unit in order to generate the tones you hear... So just to explain a little further, yes, it is the actual high voltage sparks that are making the noise. Every cycle of the music is a burst of sparks at 41 KHz, triggered by digital circuitry at the end of a "long" piece of fiber optics.... What's not immediately obvious in this video is how loud this is. Many people were covering their ears, dogs were barking..."
- found on youtube: demjp8RqDA
Joe DiPrima and Duck demonstrate, explain the technical details, and tell the history of the Solid State Musical Tesla Coil