You might recognize a few sound samples in here:
Various recordings of shortwave radio oddities, numbers and noise stations. These mysterious broadcasts are found on shortwave bands and they are - or appear to be - with no definite purpose. These signals are said to actively haunt the airwaves after World War II at beginning of the Cold War. With the collapse of the Soviet Union many expect these stations to disappear overtime but radio monitors indicate these signals continue to exist with new ones surfacing every now and then along with stations that have operated for 30 years.
So what are they? There are many speculations what these numbers stations are; theories point to covert government-sponsored broadcasts for spies abroad, illegal activities such as drug trafficking, for various scientific research and undisclosed military operations. However, to this day, no organization, broadcaster or country ever admitted the use of these stations.