Richard Gray's Power Company makes products just for that purpose. Take a look at their Pig Pole especially.
You can still buy the Mondial at "Music Direct" for $99 but there are lots of examples of these isolators. This is the cheapest I've seen:
As noted above, the Mondial device is still available, and there are other similar solutions.
Before doing anything else, I would suggest to check to ensure that the installed cable connection coming into your house is grounded correctly. Many older installations are not. If you watch current cable installation techs, (at least Comcast here in Washington) they are pretty careful to be sure to mount a gounding adaptor at the house entrance (either pass-thru or tee fitting) that has a solid ground lug connection that is then bonded to the household ground system. In many cases, this will eliminate the ground loop all by itself.
I had the same problem. This was my solution. Went to Radio Shack and bought a small plastic box, 2 switches, 4 RCA jacks and frabricated a switch box. Toggle switches turn audio signal off/on from TV's audio "Output" jacks. Needed one extra set of interconnects. Works perfectly. The reason I did it this way was because my cable reception is excellent and I didn't want to take any chances messing up the video signal.
Another approach I've used successfully: attach a ground lead to the coaxial shield at the point where it connects to your equipment. Wrap the bared end of wire around the coax a few times & cable-tie it securely, or use a small hose clamp. The other end of the ground wire connects obviously to ground: use your AC wall outlet's plate-mounting screw, or perhaps a handy ground post on your preamp, etc.
Realize that inserting back-to-back baluns results in several dB of RF signal loss: check your picture quality before & after to ensure that it hasn't degraded.
I guess I should explain my setup: I have a hdtv box from my cable company--this connects to my tv via componet cables and audio cables. The cable signal of course comes from the wall. Next comes my dvd player(Philips 963sa)which also plays my cds and sacds. I have componet cables connecting to my tv as well as audio cables.(tv had multiple in & outs) The 963 also connects to my pre for cd listening. When I want to watch dvds I have to disconnect my coax from the wall to kill the hum. Funny thing is I don't get a hum with cable box hooked up the same as my dvd player. I know it sounds confusing but it's a quick fix I'm sure. Bob if I connect a ground as you explained it would have to connect to the cable box as it loops the tv via coax and componet cables. Mind you the only coax connection is from the wall to the box. I hope I made this a little more clear for everyone. I may just wind up with the Mondial box since it was made for my situation. Stay tuned.