You have my full attention, Bob. Have you ever tried putting one ear right next to the tweeter of a non xstat speaker? Of course, like you said, with no music playing (so you don't injure your ears). With all the different systems I've owned through the years, I have always heard a very slight hissing coming out the tweeter when I did this. Call it electrons in heat, furiously rumbling around inside the electronics waiting for a signal to pass on.
Dave
MacBook(Intel)->HiFace->Anthem Pre/Pro->Anthem Amp->Paradigm Studio 100's Ver.4