My Comcast cable hum was cured from outside the house when I had my first HD cable box installed a few years ago. Twenty plus years prior the cable had been run from the pole drop into my house uninterrupted. The installer ran a new drop to a ground block which then ran into the house. He attached the ground block wire to the nearby service panel conduit.

That was a good day, HD and hum-free in one fell swoop.