In my case, I'd had a problem with a ground loop between the amp (which DOES use a three-prong plug) and the CATV line. Disconnecting the RCA cables from the TV to the pre/pro would solve it, but leave me audioless for TV. So I picked up one of those ground loop isolators and that fixed the problem marvelously.

My symptom, though, was not a hiss but a hum. A *quite* loud hum, too.

Interestingly, my grould loop isolator looks exactly like your FM trap.

------------------
Matthew J. Hill
matt@idsi.net