speaker hiss with audio aero capitole mkII

I have noticed a hiss from my egglestonworks andraII speakers that is noticeable from the listening position at the highest volume settings on the audio aero capitole mkII. The hissing comes from both the tweeter and the twin mid-range drivers from both speakers and is equal from both sp's. It gradually increases as the volume is turned up and is not present with the capitole turned off and the Krell fpb 300cx on. I have dedicated circuits with their own main panel and the capitole is connected to a PS audio P-300. The hiss is present also when the capitole is not connected to the P-300. I suspect that this relates to intrinsic noise or distortion in the capitole, possibly from the tubed analog output. Although the system sounds terrific, i am concerned that the hissing may be masking low level detail at moderate to high listening volumes. Has anybody had a similar experience with the capitole? Can this be improved? Any suggestions? Thanks.

Rafael