I have notice a noise on my second floor that seam to be coming from the wall or ceiling. I sound exactly like s wall light switch being turned on or off. A sort of click. Is is always the same degree of loudness, and happens every 3 to 4 minutes. It seams to be more frequent in the moring but doses accure all day long. My house is about twenty years old. I just started to notice it within the last month or so. Its not my PVC piping in my wall and floor, I had a plumber verify that different noise last winter. It was due to thermal expansion as hot water rain through the plastic drain pipe from my shower. I originally thought it might be duct work but the noise seems to orginate where there is no ductwork present. Could it be an electrcial issue. Im thinking about turnning off all my power to see if I still hear the noise. I am losing sleep over this. Is this a seroius problem or is it normal. If its normal I can live with it.