Check the jensentransformers.com website. It has a comprehensive diagnostic. But, to cut to the chase, chances are the ground loop is coming from the CATV line. Jensen makes a $50 isolation transformer for the CATV line that has proven to be $50 well spent for me. (No, I'm not affiliated with the company. I just happen to have spent a lot of time trying to solve a ground loop problem in my system and finding the Jensen product was a "eureka" for me. 'Sometimes it doesn't take much.) Good luck with it, Jim
