Bill get you a Mondial magic cable TV ground loop eliminater about $75 it should fix it. Search Mondial here on the forum for more detailed information
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>>What is the underlying problem<<
What is happening is there is a slight difference in the ground potentials between the house's ground plane and the cable's ground plane...current will oscilate between the two grounds, because of this difference, causing the hum.
>>can I address it differently?<<
You could tie (connect) the cable ground directly to the house ground outside at the ground rod, this way all the ground's, cable and house, will lie at the same ground potential...or you can go for the Mondial piece which will break the ground from the cable box, and should reduce or eliminate the hum.
The Mondial piece does more than just break the ground, it also cleans up the signal, and yielded better color reproduction in my system. The Radio Shack piece, I believe will probably do just as good a job in breaking the ground, but I don't think it will yield the improvement in the color like the Mondial. That's why the Mondial piece cost so much more money.
Here is info from the site
Google has many other hits for "Mondial Magic".
If you want to be sure this is the problem, a cheap way would be to go to radio shack, and buy 2 75-300 ohm baluns. The kind you used to use to hook up cable tv to an old tv with just antenna screws. Take the 2 baluns, and hook them together by the wires. Either clip off the spades and just twist and tape for this experiement, or you could just use screws and nuts.
Now plug your cable feed into one end, and run a new cable from the other end to your cable box. If this eliminates the hum, you have found the source of your problem. Then you might want to spend the money on the Mondial.
Audio Advisor sells the Mondial Magic's. If you find that you need one, look under "Manufacturers" on their website for Mondial and you will find an isolation transformer and an isolation transformer/splitter. I used the transformer/splitter and sent one output to my HT, and the other went to every other TV in my house (using less expensive splitters as needed). Hope this helps.
All Reponses here are just band aids...Your cable is not grounded to code-have them fix it. If it is not grounded with a ground block to the same ground that you ac breaker box is grounded to them you have a ground potential-basically a giant 9 volt battery that is looking for ground in between your components-HAVE YOUR CABLE COMPANY FIX IT!!!They are governed by law to do so....