From the latest issue of Wired, an interesting piece on UVB-76, a Russian short wave radio:

On the evening of September 7, something more dramatic—one listener even called it “existential”—transpired. At 8:48 pm Moscow time, a male voice issued a new call sign, “Mikhail Dmitri Zhenya Boris,” indicating that the station was now to be called MDZhB. This was followed by one of UVB-76’s (or MDZhB’s) typically nebulous messages: “04 979 D-R-E-N-D-O-U-T” followed by a longer series of numbers, then “T-R-E-N-E-R-S-K-I-Y” and yet more numbers.

From Wikipedia:

The station features a short, monotonous buzz tone repeating at a rate of approximately 25 tones per minute, for 24 hours per day. The station has been observed since around 1982. On rare occasions, the buzzer signal is interrupted and a voice transmission in Russian takes place. 

To this day, no one still knows what the purpose of the station is. Or precisely where it’s located. However, the author of the Wired piece explains:

Most observers believe that UVB-76 is an idiosyncratic example of what’s called a numbers station, used to communicate encrypted messages to spies or other agents. Typically, these stations transmit numbers in groups of five, making it impossible to detect partitions between words and sentences. The numbers can be decoded using a key in the possession of the intended listener. Numbers stations are thought to have existed since World War I, as documented by the Conet Project, a compilation of recordings that was first released in 1997. (Director Cameron Crowe, a fan of the Conet Project, used samples from it in his 2001 film Vanilla Sky.) Drug runners are believed to have used numbers stations on occasion; so too are the North Koreans, the Americans, the Cubans, and the British. Indeed, shortwave hobbyists suspect MI6 was behind the most famous numbers station on the planet, the much-revered Lincolnshire Poacher.

If you’re interested, you can listed to a feed of UVB-76 online at http://UVB-76.net.