Actually they are from the ionosphere. Well, they bounce off the ionosphere. Don't believe me? listen for yourself.
It's not really our Alien Overlords sending encrypted messages. It's just plain old spooks. It's been going on for over 30 years and I had never really heard about it. The link above does a decent job of explaining it. On the other hand, I spotted this mystery on cheesebikini:
It doesn't work now, so I guess we'll never know...
Here are some randon links I discovered ages ago but never got around to posting. Enjoy...