Numbers stations have existed since around World War I.  you can find them by just dialing through your radio and dfinding those little gaps in between stations transmitting coded messages via chanting number patterns. 

Sometimes they are read live, sometimes in Morse code, and sometimes by means of digital noise transmission. 

Chris Danger and Stat take to listening to the air waves to understand what number stations are, how they work and share some spooky stories as they go. 

Lincolnshire Poacher

https://en.wikipedia.org/wiki/Lincolnshire_Poacher_(numbers_station)

Kevin Berry’s Irish Pub

https://www.reddit.com/r/numberstations/comments/3dnshw/i_misdialed_a_phone_number_and_heard_an_odd/

The Buzzer

https://www.reddit.com/r/nosleep/comments/8865sn/im_the_administrator_of_the_numbers_station_uvb76/

Interval Signal (For NBC jingle)

https://en.wikipedia.org/wiki/Interval_signal