FWIW, I have an A23+ with an LTA tube preamp, a Schiit Bitfrost 2/64, and a Schiit Kara. The LTA runs through the Kara in passive mode, or I use the Kara for SS. A basic Furman surge protector and no other exotic cables. 

When I put my ear up to my tweeter I hear nothing. When I introduced a Schiit Lokius to my system, I heard hiss when I listened to the tweeter. When I removed it, the hiss disappeared. 

Do you have dedicated audio lines?

Mike

Thanks for the helpful hints.  I tried all 3 modes on the Freya+ and eventually shut it off, and this hiss remained.  The amps gain is set to 12 o'clock, which is what it was on when I took it out of the box.  Unfortunately it's a hassle to get to the back of it now, so I'll try to lower it when I have some time to move things around.  But since the tubes are ruled out, I suspect its that or line interference.  

The noise doesn't bother me since its nearly inaudible, and I don't listen to music with my ear in front of the speaker.  This was simply something I was wanting to learn from.  

Freya plus does the hiss on my system. Yes tubes produce hiss most of  the time. Don’t put your hears next to the speakers all good.

Amplifier Voltage gain explained – matching amp to preamp see here. 😎

Mike

My system is stone-cold, dead quiet with no audible hiss from any of the speakers set at any level.

BUT, I’m using all SS equipment not tubes. Tubes are notorious for being noisy. Especially cheap tubes.

Could also be "dirty" power or noise somewhere on the line.

If you’re bothered by it, indeed, try some cable management. You could also swap out the tubes for another brand (I quite like Electro Harmonix’s Gold ones, but have also had good results with Genalex-Golden Lion and Mullard’s upper end offerings).

You’re probably in a "try it and see mode".

From Schitt’s website:

Whisper-Silent Tube Stage—With Tube Shutdown

Now, you can enjoy a tube preamp without the hiss and hum of classic designs. Freya+ offers super-quiet tube modes with DC heaters and semi-circlotron, noise-cancelling output stages. Better yet, the tubes turn off when you’re not using them! That’s right, both the tube heater and high voltage rails go away when not in use, so you can preserve lifetime of costly tubes.

Good luck.

Move the modem and router to another room or farther away. And buy a puppy

Due to having ancient, ungrounded circuitry, I found it necessary to go against  protocol and plug my integrated amp into a line conditioner. When I turn the volume knob on my entry level amp (Cambridge Audio CXA-81) through my equally entry level speakers (Revel Concerto2 M-16's) well past 3 O'clock, I get no hiss. Even on the line input attached to an entry level phono preamp, I get no hiss and only faint hum well past 5 O'clock. Could you be experiencing RF or EMI issues? The last time I experienced hiss through any tweeters was when I using a well worn Rotel preamp.

I concurr with lowering the gain on the Parasound. My A21+ gain is set at two o'clock (two thirds). Not for hissing, but I get the best sound there.

The Schitt freya + if using tubes the hiss is from the tubes ,on position 2 SS mode on preamp it shouldnot do this.

I had that on 1 speaker when i had a Parasound JC5. But do not have it now that i have AGD DUETS.

Don't put your ear close to the tweeter problem solved. Also as stated above a little noise is not uncommon.

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. 

@akafritz Wrote:

Very faint hiss from tweeter

Lower the gain setting on the back of the Parasound A23+ amp.

Mike

Thanks for all the feedback!  Glad to hear I don't have a problem, perhaps aside from a need to do some cable management.  

IME, a system with tube electronics likely produce a faint hiss; which is normal. As long as the hiss noise doesn’t intrude or increases as you raise the volume or audible from your listening chair, you got nothing to worry. If it bothers you, then be ready to spend some money and considerable efforts on gear swapping journey.

"if I put my ear very close to the tweeter on either speaker, there is a very faint hiss sound."

Avoid future audio neurosis- don't put your ear up to the tweeter.

Best long term solution for A.N- stay away from audio forums.

All of my systems have had some sort of very faint hiss when no music is playing, and I put my ear right up to the tweeter. It’s a good way to confirm that the tweeters are working, and should pose zero issue when listening to music.  No problem if it's not loud enough to be heard across the room, or when music is playing.

It normal in most cases . Turn the Amp on without the preamp.   Still there?  Normal to some degree, depending on speaker.   Try to make sure interconnects and speaker wires are apart and also not intertwined with AC or ethernet. 

Still exist?  Try different tubes in the Schiit