Go outside and look where the cable company's cable attaches to the house. Do you see something that looks like a splitter with a wire connected to it. This a a lightning arrester. Does the wire that is connected to the arrester go to a ground rod driven close to the arrester. If yes more than likely this is your problem, a ground loop. Disconnect the wire from the arrester and see if the hum is gone. If is is gone you still will still need lightning protection. Run a new wire from the arrester to your main incoming water line. Use a water pipe ground clamp. If you cannot get to your main water line connect it to a cold water pipe of your water system.
Jim
Jim