I considered this a possibility. I live in a new building that has fiber optic from comcast. I disconnected everything from the cable line coming out of the wall and pulled off the panel to the coax routed to my living room. The fiber optic line has to be powered so there was a plug within the panel. I disconnected that as well to see if it would change anything.When I installed the new AVM processor and McIntosh amp it was around the same time that Cox, my cable company did a major upgrade. I was getting some serious hum and a 3 into 2 plug didn't work at reducing anything. I installed an inexpensive Viewsonics Isolator model VSIS-EU between the cable box and the cable coming out of the wall and it did the trick 100%. Maybe this will help someone.
I dont have a comcast box or sat box at all. the coax goes right to my modem and ends there. This all had no change to the noise from the speakers. Its been a frustrating week. You know it'd bad when the wife asks you "what are you going to do with that 50lb paper weight you just bought for $600?"