I can speak for the appliance module. I use one to control my fireplace, and all u hear is a click when u turn it on or off. There is no hum, because all the unit does is either make a connection, or turn one off. Personally, the click doesnt bother me, its definitely not what i would consider silent, but i really barely even notice it if im watching tv. I use the X10 universal appliance module. I know there are more out there that might be quieter, but once again, its just a click...nothing that bothers me.