The first time you put them in the residential lot, they work fine (without music notes if there is not stereos on in the lot) but once Sims turn on a stereo in the house, wall speakers always seem that they are "working" with music notes coming out of them even if all stereos are off in the lot. Yes Emma, it's weird!
This is the way they work in my game as well. I have stopped using them altogether for this reason. Additionally, if they are farting notes when installed outside, and you have a party, even if the stereo is off the police will come around to break up the party when it gets too late (around 11:00 or 11:30pm).