What does it sound like when we fall asleep? Are there hypnagogic sounds to accompany the fleeting images you see as your brain tries to shut down? The closest thing to it in the waking world is shortwave radio.
For those who don't know, nearly every nation has broadcast signals in the shortwave spectrum for decades. This portion of the radio spectrum lies right beyond your AM radio dial, starting at about 2kHz. These signals do not lose strength over time the same way FM or TV broadcasts do, so if we trawl the waves (especially LATE at night), we are often treated to something broadcast from VERY far away.
I've been addicted to my shortwave since I first heard the sounds of WWV - the 'time signal' station - in the 70s, and compulsively record transmissions now as a way to.. stay sane.
I had a podcast going for a little while in 2006, dedicated to sharing this stuff. Here are two 'episodes':
Apparently there was a relay tower in California which repeated a Greek station's daily broadcast. In Ballard, with a minimal antenna (made from a slinky), I was able to pick up audio as strong as a local AM station. With better music.
I have used a number of beats in this clip in films elsewhere. It's one of the main sources of sound in a short I did by Reed O'Berne, Soul Gold.