ARC LS25 mkII noise level

If you are listening intently from three feet away and worry about the noise. You are not having any problem. Tubes ALWAYS make a little noise.
Anyway if you can't stand the thought that your preamp has a very slight hiss that you have to get right up near the speakers with no music on. The agree tubes are not for you.
Tubes make noise. Good tubes make less noise. Bad tubes make a lot of noise, more than yours are doing.

Yes, there are tube dampers on the 2 6h30s. They are the UltraSonic Hal-o dampers. I will work with ARC to resolve this. It might just need some service.

@Elizabeth I wish it was 3 feet. 3 meters which is about 10 feet away from my listening seat.

It's more of a hum with some hiss and a slight buzzing. I've ordered new tubes. And I'll disconnect all the sources one by one to see if that helps. The spec sheet says 14uV IHF weighted so on paper, it should be nearly dead silent.

Also, try to float the AC ground on the LS25 temporarily. See if the hum/noise go away.

The guy you need to talk to at ARC is Chris Ossana. Helpful and technical Guru.

I have a pair of Classic 120's and Ref3 LE both with many upgraded parts in the critical signal path and power supplies. When the amps are on and the Ref3 is off, there is absolutely no noise or hum coming out of the speakers.
When the Ref3 is turned on and i select any source (except phono) with no signal and turned the volume to the max, there is only a very faith hiss that i hear when i put my ears to the speakers. Selecting the phono input while the phono stage is turned on with no signal, i can hear hiss or what they call "tube rush". However, that is to be expected from tube phono stage. Mine is a Ref2 Phono.
Tube amplification nowadays CAN BE quiet although no quite to the level of a good solid state design.
Good Luck.

I did float the ground on the ls25. Also on the power amp. No change. I'll test by disconnecting all sources one by one to see if there is any change.

Your setup's noise level is what I would expect. I do think there is something going on here on mine. But if I take the LS25 out and replace with a solid state preamp, the noise is gone.

I have the LS-25mkII and have had it for about 5yrs. and have never had any issues with noise. I'm talking standing right next to speaker with ear to tweeter!
Sounds like it could be in the power supply(just guessing)
If you can do without for about 3 weeks, I would send back to ARC.