What's that noise?

I agree with the others that it's nothing to be concerned about.  The cause could be what George suggested, or it could be the inherent self-generated noise of the input stage of the preamp amplified by everything that follows (any electronic circuit inherently generates a non-zero amount of noise), or it could be noise introduced into the preamp as a result of a ground loop between it and the source component (ground loops can cause high frequency noise as well as low frequency hum).  Or it could be a combination of some or all of these things. 

Contributing factors are undoubtedly that your speakers are more sensitive than average, and the gains of your preamp and power amp are a bit more than average. 

Regards,
-- Al
   

Thanks for the replies. The speakers are Legacy Audio Focus rated at 4 ohm and 96db. The "noise" does stop just below full volume and there is no way one could listen at this level. I usually don't use more than about 33% of the potential volume level.

Me either.

Hard to  be certain w/o knowing what kind of speakers you have or what their efficiency is and how far away you are standing, but at full volume you hear a little white noise, that does not sound unusual to me.