...way back when, a lot of sound cards had a connector on the top which could be hooked up to your CD drive, so that the drive could play Red Book audio which w

...way back when, a lot of sound cards had a connector on the top which could be hooked up to your CD drive, so that the drive could play Red Book audio which would be sent (as analogue) to your speakers. Clever me noticed that the pinout of the CD drive matched the pinout of the PC's internal speaker. Aha, I thought; I can connect it up so that the internal speaker noises come out through my sound system. Turns out that full-voltage square-wave 5V, amplified and pushed through a set of decent speakers, is... slightly loud. (I was actually lucky not to damage the speakers. Or have a heart attack.)