Musical Spark Plug
I had to meet with a client to test if my flare stack ignitor controller worked. I used a spark plug and coil for testing. One after another, I started to play with the pulse pattern to monitor energy usage vs spark power. I then recognized tones in the spark. The sound/music you hear is coming from the plug's spark at controlled frequencies from my circuit.
I modified my code and made the spark plug sing. I tried to make it play twinkle twinkle, but the tuning is off :)