I'm not positive, but I think the "standby" in your Cary may be the same as a "Mute" which means no signal at all is passing out of the pre to the amps. Puzzling though about the Classe SS preamp making the same noise as that eliminates a tube or tubes as the culprit. When you say "White Noise" are you talking about a hissing or 'rushing' sound, or a humming sound? I assumed it to be more a hissing/rushing sound. If it is a hum that may be as simple as a ground loop problem, where you could try floating the ground on the AC connection(s) using a cheater plug (3 prongs go in, 2 prongs come out).
Marco