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

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.

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

Mike

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.

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.