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.
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.