My PC speakers do that. I'm pretty sure that's the cable between the sound card and the amplifier acting as an antenna and picking up the broadcast as interfere

My PC speakers do that. I'm pretty sure that's the cable between the sound card and the amplifier acting as an antenna and picking up the broadcast as interference. Then it gets treated by the speaker system as if it was the actual audio signal. Here's the thing, though: either AM or FM, radio broadcasts are definitely not in the human hearing frequency range. EDIT: Thinking about, maybe what he meant is not that the carrier signal is in the sub-20 kHz range, but rather that the switching happens at around that frequency. For example, gates opening and closing modulating the amplitude at audible frequencies.