Faint speaker hiss

Was wondering if anyone here might be able to help me out. I recently acquired a new naim integrated (XS2) to pair with my Harbeth p3esr. I am using straightwire speaker cables which I've had for years. I noticed when I plugged everything in that the speakers have the ever so slightest hiss coming from them. I cannot hear it unless I get extremely close to to tweeter and te sound becomes non-existent once music starts playing. I have had the amp for about a week now and have kept it on 24/7. Does anyone know where the small hiss could be coming from? I tried different speaker cables/power cord and that didn't change anything. I also tried unplugging all my sources and left just the amp and speakers plugged in ad still had the faint hiss. Like I said, it's not audible unless I really get my ear close to the tweeter (about 3 inches). I might be nit picking but was wondering if anyone has had experience like this before? Should I try a different outlet? I am in an apartment so only have one or two places to put everything. Any help would be greatly appreciated. Thanks!
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?