I have a Denon AVR-3806 which sends the front left and right signal via the pre-outs to my Adcom Gfa-555. It also sends the rear and surround signals to two Adcom Gfa 545s (I am runnig 7.1). I have recently noticed that my front right and left speakers (RTI 8s) have a faint hum in both the midrange drivers and the tweeter. My rear and and surround speakers produce no such hum. I swapped the 555 with a 545 and the buzzing vanished from my front speakers. I then unhooked the inputs from my 555 with only the speakers connected and the hum disappeared. Is this ground loop noise coming from my 555 or could there be something wrong with the 555's inputs? Again both 545s are dead quiet. It seems the 555 just doesn't like my Denon's pre-outs. Any help is greatly appreciated.