Leningrad Military District

It has been interrupted and stopped many times, yet no retaliatory response, nuclear weapons, nor intercontinental ballistic missiles have been launched as a result.

The best supported theory is it's part of a military command network for the Leningrad Military District of Russia.

So, essentially, it's a radio station that is constantly releasing just a buzzing tone and sometimes a name or some words in Russian.

And no one's really sure what it does or where it's coming from.