 There is speculation published in the "Russian Journal of Earth Sciences" which describes an observatory measuring changes in the ionosphere by broadcasting a signal at 4625 kHz, the same as the Buzzer.It is also speculated that the voice messages are some sort of Russian military communications, and that the buzzing sound is merely a "channel marker" used to keep the frequency occupied, thereby making it unattractive for other potential users.The signature sound could be used for tuning to the signal on an old analogue receiver.