Are you sure the humming is comming from the speakers?
Listen to the voices
"They're comming to take me away he he ha ha.
They're comming to take me away he he ha ha.
To the funny farm, where life is beautiful all the time.
They're comming to take me away he he ha ha.
They're comming to take me away he he ha ha."
Now to fix your problem.
Sounds like a ground loop. Have an electrician check the wires. Did the switch you installed have connections for two wires or three?