The homemade version helps. It reduces noise level tremendously. Yes, I live in a horrendous RF polluted environment, NYC. Even when people walking in the room, the noise level changed, NOT ANYMORE!
It all began 3 months ago when I installed my preamplifier into my system. The annoy HUM jumped out from speakers! Moved cable TV to the other room and cheated all, except one, plugs, the noise was reduced but still noticeable. Last week, tried to cover all unused RCA connectors with surplus interconnect cables without connecting to anything. I AM PACIFIED AT LAST.
I am open to any suggestion(s). But if you have the same problem as I did, try inexpensive surplus interconnect cables that come with TV set or DVD player for temporary solution first before spending money on Cardas RCA cap.