Noise from tweeter

Could be mains noise. I get this on my Avantgarde Duo horns drivern by Quad IIs. Late at night is much better as I don't pick up mains noise from either electrical appliances in my home or even from other houses up my street.

Unsound is absolutely correct! TI based Equibit digital amplifiers are as quiet as it gets. No Hums ,no hiss..nothing ! They have a hard mute built in so they put out no wattage ..unless a digital bitstream is sensed. The PCM bitstream is changed to PWM form and then filtered and buffered.The signal is sythesized directly on to the speaker terminals which creates a high powered D/A converter.No traditional D/A converters are used in the audio signal path.
In laymans terms these amplifiers are just high powered Dacs that plug directly into your speakers.
This is also an open loop design no feed back.
At the present time there are only two audio manufactures that use this technology Tact all digital amplifiers($10,000 price range) and Panasonic all digital amplifiers ($300.00 price range).
Here's a link for the ones that want to understand this technology and not confuse it with amplifiers that are not 100% digitally based.
http://www.classd.org/

I don't know from personal experience, but, it's reputed that speakers hooked up to digital amps don't demonstrate this propensity for ear to tweeter hiss.

Perhaps you might be extremely sensitive to the noise. It has nothing to do with the tweeters...for you seem to mentioned that you had a different amp before. Try switching speakers to hear whether you can hear the same noise as you presently do. When you do this, try to arrange to get a speaker with the relative same SENSITIVITY, for you would not want to compare apple and oranges, sensitivity wise.

I have gone from very dynamic and insensitive set up to a very quick, sensitive and low power set up.

My set up about 6 months ago was 4 speaker system, two monitors on top of two passive subwoofers (Gershmans) at 88db sensitivity, paired with a First Sound Presence Deluxe I as well as a McCormack DNA 225 weighting in at 200 watts/channel. There was not power conditining anything back then. The noise, with my ears next to the speaker was very low, a little hiss. This, I think was unavoidable.

About 5 months ago I went to a 20 watts integrated set up (47 Labs Shigaraki) which I think has a passive preamp stage with a very potent op amp stage, all connected into
1- a pair of EPOS ES 11, 2 way monitors, biwired at 89 db with just one cap between the mid/woofer and tweeter.

This set up was very quiet, and I needed to crank the volume up a little in order to get very dynamic sound. With my ears close to the woofers, I could hear a little hiss....without anything playing, with the amp on.

2-I connected the Shigaraki to a pair of Fostex 208 Sigmas at 96.5 db sensitivity, no crossovers.
At this point, I could hear more of a hiss, which I think was due to the gain from the Shigaraki integrated as well as a major increase in sensitivity of the speaker.....at this point in time I was running my set up with a BPT 2.5 deluxe edition, with bybee etc.... Still, some hiss.

Now, I run the fostex with a FINAL Music 5 and Music 6 preamp/amp totally battery powered, no hooking them to the BPT.

Noise? Yes, still hiss, which I suspect is due to the gain of the preamp and the sensitivity of the speakers.

My point is that, the hiss that you might be hearing from your speakers might be induced by multiple factors:

Either, sensitive speakers.
or
bad cabling....(actually, I had more noise that came through the speakers when I had a powered subwoofer wired with banana speakers sharing the same speaker binders of the amplifier...this set up introduced a noticeable electrical noise, still inaudible from listening position, but very noticeable from about 10" of the speaker.) In order to get rid of this noise, I swapped three set of speaker cables, as well as two pairs of interconnects....until today, when I was once again able to get the subwoofer integrated with a pair of Analysis Oval+Cardas/Radio Shack spade-banana adapter.

Once again, there is hardly noise...same as having no subwoofer connected to my set up.

I think I am just becoming darn picky as I get older (just 32 now) because I think I have sometimes I expect a certain quality for the price.

The noise is more of a static noise, as opposed to a hum. Thank you, Henry

Do you hear distortion when playing the music?
To check it more clear turn on quiet the music preferably with emphisized cymbals and alphas and listen closer to the tweeter. Vary the volume safely to hear distortions go up or don't appear at all.
Also you can check the same with piano passages. Play some Revolutionary Ethude of Chopin. I have Vladimir Ashkenazi Ethudes on London records that is my reference piano recording.

There is going to be some noise (HISS sound); it won't be dead quiet. If you have to put your ear right up to the tweeter to hear the noise, then it might be normal....

Now if what you hear is a low HUM and not a HISS, then it could be a "ground loop hum" problem. It can be fixed by removing the electrical AC ground on the component causing the problem (I assume the amplifier in your case). The way to test it (and fix it quickly) is to put a "cheater plug" on the AC power cord of your amp (or the component causing the hum). A "cheater plug" is one of those adapters that allow you to plug a 3 prong AC cord into a AC socket without the third ground input.

Assuming it is a ground loop hum and you do not want to use a cheater plug with a high end power cord as a permanent solution; you could take the power cord plug apart and disconnect the ground wire. If you are not comfortable with this, some audio power cord makers will make you a custom cord with the ground disconnected.