For decades, short wave listeners have been hearing stations that do nothing but read blocks of numbers, usually using a woman's voice, in a variety of languages and on innumerable different frequencies. All available evidence indicates that some of these transmissions may be somehow connected to espionage activities. These are the numbers stations, the most enduring mystery on the shortwave bands. More info
Some artists are using snippets from number stations transmissions for theire own tracks. Fans of Scanner, Merzbow or Autechre may even like to listen to them un-edited :-)
Just follow the links below to find mp3 recordings.
Links:
The most comprehensive webpage, links and downloads