Hiss noise from speakers

I think you are simply hearing the background noise of your amps. If you can't hear anything from your seating position, I wouldn't worry about it. Many amps do it.

I can only hear it when my ear is next to teh tweeters. And, as mentioned, only when pre is on. Don't hear it when only amp is on. So, this is common among separates?

The problem is not exclusive to separates -- integrateds and receivers do the same thing. As Aball said, it is pretty common. That said, some preamps are more noisy than others and many times the noisier ones sound better (but not always). But if I had to choose, I'd pick a moderately noisy piece that sounded good over a quieter piece that sounded worse. Perhaps you will find a quiet preamp that also sounds good...

Just to further complicate things, consider that the noise could be from any piece of gear in the front end of the system. Try the preamp switched to an input that has nothing connected to it and see if the noise is the same. If it's lower, then the noise could be coming from your source component and not the preamp. Also, some audio cables exhibit more hiss/noise than others...