What cause tweeters hiss ?

@auronthas 

I am very surprised, assuming you are saying that when you select CD input on your amp/preamp and turn the volume up with no signal you do not hear hiss; whereas it is audible when you select other inputs and do the same.

I am not clear how the selection of a different input can alter the noise generated by the (power)amp.

Re your initial post, I don't think hiss is likely to be caused by grounding issues; they invariably lead to hum.

And, frankly, DACs can cause all kinds of issues.  I regard them as the black art of digital sound reproduction and its Achilles heel.

I don’t think it’s the tweeters. 

@clearthinker When I tested with the CD player, I isolated the DAC power supply, CD player using RCA out to Integrated Amplifier , no hiss.  

I just tested my Ares II , removing both toslink and USB input, hiss is still there , it is very minimal though.  I will leave it now.

Thanks guys for your input and sharing. 

not a ground loop. ground loops occur at 60 Hz (or 50 Hz in most parts of the world). Not tweeter frequencies. A ground loop is essentially a "signal" caused by the difference between two different ground reference points being amplified.

Can you explain this again from the beginning? We are all missing something

When you refer to "power off", what precisely are you powering off?  The accuphase?  The denefrips?  Pls be very precise.

Is there no preamp in this system? I see no mention of it. Or I missed it.

What about with no input to the [preamp?  magic box? whatever is before the volume] whatsoever?  This is the "null hypothesis" and reveals the amp / preamp hiss.