Suddenly the piercing buzzing noise that has continued incessantly for months stops. A cold voice takes over. ‘U-V-B-7-6,’ is read out in a thick Russian accent, before listing a series of code words and numbers. Then, just as suddenly, it ends. The buzzing returns, for another few months. That is what has greeted listeners of a mysterious radio station nicknamed 'The Buzzer' - and code named UVB-76, or more recently MDZhB - since the 1970s. But what the Buzzer is doing, or who is broadcasting it, remains a mystery - with theories ranging from the Russian military to atmospheric research....