My experience with a CJ ET3-SE was a soft white noise exactly as you described. Tubes do have a higher noise floor than SS, but the noise (I call it SHOT noise or thermal noise) seem perfectly normal with tubes. In my situation, the shot noise seemed to be "fixed" so as the volume went up, it falls farther and farther into the background. Turn your volume knob "up" and the noise should seem to stay about the same, in other words. This is why it isn't too bad with music playing. Eventually, the tube went bad, and made a scratching or sizziling sound in one channel...time for a new tube.
Go here for some tube basics on noise. I think your unit is just fine.
http://www.john-a-harper.com/tubes201/#Noise
Go here for some tube basics on noise. I think your unit is just fine.
http://www.john-a-harper.com/tubes201/#Noise