In addition to the Marantz Professional, partner Eirin and I experimented with the Telephone Contact (Suction) Microphone, which captures electrical vibrations only.
We began with the television, desktop, and mobile phone. It was interesting to hear that each item had its own frequency range and harmonics; however, I’m so glad that the human ear is unable to hear these sounds because they were pretty terrifying.
We then moved upstairs to try the refrigerator. Somehow we tapped into a radio channel (?), and we were able to capture a station playing orchestral music.
We were both amazed and horrified. Take a listen!