Background radiation is everywhere and it can be affected by the environment. Very big planets like Jupiter can emit radio waves. Smaller planets and moons are more likely to reflect them rather than emit them. I was listening to a few clips from a website recently (of sounds from Earth) and the description was that the sounds (in that particular video sample) were coming from electrons travelling along the contours of Earth's magnetic field. Another source of the sound in the videos is the effect of the solar winds buffeting the planet's electromagnetic field.
So it's not only radio waves, but also electrons and other waves and particles. I just used the radio example to help describe that it wasn't sound being picked up but other kinds of energy and particles instead that were being converted into sound, the most familiar example of that is a radio setup.
So it's not only radio waves, but also electrons and other waves and particles. I just used the radio example to help describe that it wasn't sound being picked up but other kinds of energy and particles instead that were being converted into sound, the most familiar example of that is a radio setup.