Try it. It is most definitely the fluctuations in the light. Yeah, there is likely some EM interference, but the rapid fluctuations of artificial light are the

Try it. It is most definitely the fluctuations in the light. Yeah, there is likely some EM interference, but the rapid fluctuations of artificial light are the source. LEDs, CFLs, even incandecents, all have vibrations that are audible when you pull audio out of the solar cell. Sunlight, not much. No audible vibrations at all. IR remotes are fun. For the last show I played, I put a couple layers of garbage bag over the solar cells to make an IR pass filter to block the stage lights from interfering. Really, give it a try.