Ever since I was 10 (and that was 42 years ago) I've heard this sound on shortwave radios. It occurs at lots of different frequencies here in the UK - for example, 3.39 and 4.57 MHz. I've just listened to a remote German radio on 3.39 MHz, and its there as well, so it isn't that local. Sometimes it fades in and out - like everything else on shortwave radios, but I've never known it to disappear completely while I've been listening. It seems to be ever-present. I have tried listening to a remote Canadian radio - and I'm not sure if I can hear it there or not.
What on (or off) earth is it?
Shortwave Sound by Dominic Rivron
4 years ago