Hi, I have a Harmon/Kardon AVR 325 7.1 Channel Receiver. In the Front Left, Rear Left, and Center Channels there is an aggravating amount of distortion and when there is no input there is a faint hiss only in these channels. I know that it is the receiver itself, not the speakers or the cables. Has anyone had this happen before? Is this a common problem? Can I fix this without having to replace the receiver?