Terry Yager
Veteran Member
Flowing current can make noise all by itself. It's the same principle which makes an AC transformer hum and the flyback transformer in a TV set squeal. I have a Sony Walkman which has no built-in speaker, but if you unplug the headphones and turn the volume all the way up, you can hear a faint, tinny rendition of the audio -- the circuitry inside the Walkman itself is making the noise!
Remember the first electronics project you (ie, almost all of us) ever built...that crystal radio...?
--T