Well it doesn't back onto a bathroom so it's not a shaver socket and we don't have a burgler alarm. The wall the hum comes from is an outside wall and we initially thought it might be coming from the TV ariel booster as it is near that bedroom. However, tracing the sound to the sitting...
I have a 10 year old timber framed house which is a self-build (not by me).
There is a loud humming sound from behind the wall in my daughters bedroom. Have tracked this to the electrical circuit which feeds the hallway and the sitting room lights. Sitting room is directly below her room...