Quote:UZB76 (sometimes referred to as UVB76, but recently MDZhB) is the call sign of a shortwave radio station that usually broadcasts on the frequency 4625 kHz (AM suppressed lower sideband). It is known among English speaking radio listeners by the nickname The Buzzer, and by Russian listeners as Russian: жужжалка 'the hummer'. It 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. Despite much speculation, the actual purpose of this station remains unknown to the public.

http://en.wikipedia.org/wiki/UVB-76