In Stranger Things Series 3 episodes 1 and 2 the characters are dealing with a radio transmission.
They identify the source of the transmission from the music included in the audio.
That source is the mall, specifically the ride-along-horse.
How does the music from there into the transmission?
We are shown the radio room is a long way from the shopping part of the mall later in the series.
There is no mention of any microphones or surveillance of the area.