All my life, I've tinkered with electronics. Often, this involved finding odd bits, not knowing what they were or if they worked, and trying to hook them up to do something. One easy thing to do is hook a speaker or earphones to something and see if it can make (or receive) some sort of sound. Many times, I'd hear the same sound. Sort of a reverberent, ringing, pulsing, singing sound. At first, I thought it was the Universe trying to talk to me by any path it could. Later, when I first came across the phrase "music of the spheres", I thought "That's it!"
I hadn't thought about it in a long time, but this post, by twistdfateangel reminded me of it.
I vaguely remember that I heard the sound once on a recording. I was recording the sound from an old tube TV (tube electronics always seemed best for it) the old bad way of holding a microphone up by the speaker. And years later, when I was listening to this otherwise-unremarkable recording of TV audio, I heard a snatch of it in a quiet space in a Dr. Pepper commercial "We're Peppers, too! [*] I'm a Pepper, you're a Pepper...". The asterisk marks where I remember hearing it. I should see if I can find that tape and see if I can digitize/share the sound. I won't be surprised if it can't be digitized. I was surprised it could be recorded at all.