Faint speaker hiss

It is a minor constant sound that goes away once music is played.

You're welcome. Note, however, that the hiss doesn't "go away". It's simply masked by the relatively much louder music. Hence the hiss is simply one component of your systems overall "noise floor".

Hi mgreg42.
This is great question that I also want to learn answers..
1-Try unplug all rca inputs(source or preamp isn’t connected) & Short your rca inputs of your amplifier.
If you hear a noise from your speakers it should be the noise floor(SNR=signal to noise ratio) of your amplifier..
I do not know unshielded speaker magnets can cause a hiss or not..
2-Try to play an empty(no music in it) flac or cd file from your system.You can find the file on internet.(google it).I also have the file in my computer.If you can’t find I can send it to you.
You said noise is gone when music is starts.Check the 2nd it really diseappers or not.

If when music starts noise is gone it is probably normal.Because when nothing is playing some source equipments shorts its outputs automatically any possible noise can get pass to amp is eliminated automatically.
Even output shorted some noise can leak to your amp..

There are some amplifiers with fancy S/N
like the benchmark ahb2 like 132db.

Reall issue here we don’t listen speakers like sea shell but we want to be SURE the hiss noise is really normal or not..
This is my first post in here..

Speakers themselves do not make any noise. You did not mention what source/input you were using. The phono input is always noisier than the line input as it needs more amplification.

I looked at the manual of this naim amp:
"3.4 Radio Interference
In some circumstances, depending on where you live
and the earthing arrangements in your home, you may
experience radio frequency interference. Controls on
broadcasting in some territories allow very high levels of
radio frequency radiation and both the choice and exact
siting of equipment may be critical. Susceptibility to radio
frequency interference is related to the wide internal
bandwidth necessary for high sound quality. A radio
frequency filter kit is available for some Naim equipment but
sound quality will be progressively compromised as more
elements of the kit are fitted."
Maybe this can also help?

There is also a good article about noises:
https://www.gcaudio.com/tips-tricks/system-noise/