Perhaps try the Freya+ in one of the other non-tube modes to see if the hiss remains. If the hiss disappears or is lowered dramatically, it may just be some tube noise flowing through the system.
Very faint hiss from tweeter
I just put a new system together and noticed that when no music is playing, if I put my ear very close to the tweeter on either speaker, there is a very faint hiss sound. Is this indicative of a problem? Its not audible unless my ear is very close to the tweeter, but I wonder if its polluting amplified sound when I play music. Should a system be stone cold silent when powered on with no music playing?
Heres my stack:
Focal Aria 936
Parasound A23+
Schiit Freya+
Bluesound Node X