Listen to a minute of this, from about 0:50 onwards: The Swedish Rhapsody (MP3).
This spooky sound is sampled from a Numbers Station. Hundreds of these shortwave radio stations exist around the world, transmitting numbers, letters, beeps and simple tunes. Their origin – and ongoing transmissions – still largely remain a mystery.
Are they secret codes and directives for spies in foreign countries? Are they sources of misinformation to distract the enemy? Perhaps messages between druglords? Hoaxes by amateur enthusiasts? The answer is probably: yes, all of these, and more besides.
The Conet Project sampled 150 transmissions from 20 years and released them on a 4CD set (“Not available in stores!“, I suspect). This is currently “out of stock”, but the recordings are also available on archive.org, should you wish to disturb yourself some
You can read more about Numbers Stations on Damn Interesting, and Boing Boing’s coverage of the copyright fight between The Conet Project and Wilco, who used a sample of the recordings on their Yankee Hotel Foxtrot album. Wikipedia also has entries for some individual stations, including The Lincolnshire Poacher, Cherry Ripe, and UVB-76.
Lego spy photo under Creative Commons license from Flickr user Dunechaser.