What naturally occurred radiations or waves that don't produce any sound at all regardless of frequency and medium? In the video below, this person, Donald Gurnett and some other people at University of Iowa claimed to have recorded "sounds" from space. What producing those "sounds", they said, are plasma wave and radio wave. Is that real sounds afterall or is it just artificial sound produced by audio devices? But personally I don't think plasma wave, radio wave and any other EM wave produce any sound at all regardless of frequency and medium because EM radiations are much more different than sound wave.
At 02:12 the video does clarify that these are not sounds we can hear:
"Strictly speaking, [Voyager's] plasma wave instrument does not detect sound. Instead it senses waves excited by electrons in the ionized gas (or plasma) that Voyager travels through. No human ear could hear these plasma waves."
The Voyager spacecraft plasma wave instrument is designed to operate from 10 to 56 kHz, making it sensitive to a type of longitudinal wave similar to acoustic waves. These are called ion-acoustic waves.
Actually the University of Iowa has been publishing on similar data since the late 1970's - using spectrogram plots similar to those in the linked video, above.