remember, the 7500 was biamping the LSi15's (fronts). I decided to switch the upper drivers on one of them to be driven by the 2200 which had been driving the rears. Everything is on a component rack and I use the holes in the back to snake the cables through. When I made the switch, the hum was gone from that particular speaker's tweeter and replaced with a slightly more acceptable his. At this point the only thing left to test would be the brand new AudioQuest Type II speaker cables but I doubt there is any problem there. My fear is that something is slightly amiss with the 7500. I am also going to try routing the 7500's power cable away from the interconnects with which it share a hole.