Please I need urgent help. This is a new product. This consistent humming/buzzing sound happens when I turn it on using switch on the back, or by plugging in. This subwoofer has automatic shut down feature. So it shuts down in 15 minutes after turning off the receiver. There is no buzzing, humming sound as long as it automatically shuts down and turns on. Whenever I shut it down or plug out, the noise comes back when turn it on. Is this normal or my sub is defective? Oh also I should note that, I tried to plug in to almost every socket in my house. Noise was there. (Sub's not connected to anything else.) But switching input from "LFE" to "Normal" makes the noise go. (whether it's connected to the receiver or not.) Your help is much appreciated. I do hope my product is ok, I was just missing something or this is normal.