I had the electric company install the whole house protector at $5 a month and all was fine for a couple years. Then started to have a low level hum in my system that I could not find. Finall had the utility company out and found the surge protector was not mating with the new automated meter reader they had installed. After 3 different automatic meters, which transmit the meter reading to the co. upon a prompt from them, they removed the surge device and the hum went away. They told me it was a compatability problem with the new meter and the older surge divice. But the tech told me that many of the surge devices deteriorate over time and can cause a hum in sensitive audio equipment. So if you are having a low level hum you cannot find---take a look at your whole house surge divice as well as the cable line and all the many other things that can cause a system hum------