Audio Research REF3 / REF110 owners...

Are your REF3 and/or REF110 free of any "hiss" or background noise?

I heard the REF3 without the REF110 and it was a dead quiet background. When the REF110 was introduced, there was an audible hiss in quiet moments in the music... this is a concern, but perhaps that particular unit needed some attention.

I didn't mention anything to the dealer b/c I was so blown away by the music, but I couldn't live with any hiss or an unquiet background (don't know the correct terminology).

I've been running this combo for almost a year now and it is very quiet with no audible hiss from three feet away from the speakers. Sounds like the amp that you listened to may have needed a tube replacement. The AR gear has been rock solid in my system.
THat's why Halcro rules
I use Pass Labs X-600 solid state amps with my Ref3. The Ref3 is dead quiet.
Ref 3 is dead quiet also on 19 years old Rowland 7M monos. Better get that 110 looked after. Guido
A normal working example of the REF 3/REF110 combo will not have that level of hiss or tube rush audible from the listening position. I agree with an earlier poster that you have a bad tube, likely one of the small signal tubes that is causing the excessive noise.

I would guess that if you listen carefully, the noise is coming from one channel rather than both. If this is the case, swap the small tubes from one channel to the other and see if the noise moves. If it does, then you know what which tube(s) to replace.
My Ref3 got a hiss on the left channel. Switching tubes ( V1 and V2) made the hiss go to the right channel. So it was a tube problem. Replaced the tube and the problem was gone.