As many of us know in the electrical/electronics world, all home electronics equipment has a form of filtering associated with the a.c. line and/or the filtered d.c. down the path. Series noise filtering can be a line transformer as you would find on better equipment or an rc network as found on direct line connected equipment.
I see these "line conditioners" in the stereo/tv stores selling for as much as $500.00 to $1500.00. These units clean-up noise as well as stabilize the 120 volt line voltage.
As I have come to understand, the need for these units is grossly exaggerated by salesmen to unsuspecting customers, as the line noise levels are already reduced to acceptable levels in the tvs/stereos in general.
I want to disclose the brand you might be thinking of, but well...
Dave M.