This reminded me of a funny story.
The house we lived in when I was a young kid had an intercom system. It was a convenient way of getting five kids to come to dinner etc. So we sold the house and eventually one of the next owners, rather than removing the system or unplugging it, simply wallpapered over it.
Fast foward a number of years, my neighbor next door, who still lives there, is a HAM radio enthusiast. Due to the age of the intercom system, it would occasionally pick up the signals from his HAM radio. The people thought the house was haunted because of the muffled voices coming out of the walls.
Funny enough, it didn't even happen when he was using it. It was picking up random signals from all over the world so sometimes the voices would be speaking foreign languages.