Violin, Viola,Cello background noise

Can anyone identify the quiet, but obvious "shushing" sound found to some degree in all CD recordings of string section performances? It seems to be most apparent in sonatas and other chamber music. I can notice this sound with all my speaker sets, CD players, and amps, both tube and solid state. The sound is present to some degree from every CD manufacturer regardless of whether the recording is DDD or ADD.
It is probably in all recordings, you just notice it more when the music is quiet.

There is white noise added to most digital recordings called Dither. Dither is a form of noise, or 'erroneous' signal or data which is added to sample data for the purpose of minimizing quantization error. Dither is routinely used in processing of both digital audio and digital video data. Jitter is not synonymous with dither. Some CD players have adjustable dither.
Could it also possibly be the sounds of the bows on the strings (close-miking can reveal this, particularly with smaller ensembles)? I'm not really sure what the sound you're describing really is until I hear it.
I do believe if your system is "resolving" enough, this kind of noise could possibly just be the microphone picking up the acoustics (surrounding air mass) of the room in which the recording took place... ie: shushing noise...
I can list many examples but I am unsure which recordings I would have in common with you. The ECM recording of Schumann's 1st and 3rd string quartets
(2003) is a good example. The sound is apparent throughout the CD but is very noticable during the 1st 30 seconds.
Nose hair.
I don't think it is dither. Dither is only toggling of the least significant bit, which, with normal gain, is not audible, and would be a pure tone, not a "shushing" sound.

Even with a digital master recording some analog amplification of the microphone is involved, and might contribute some noise. More likely, the analog stages of your digital source may be noisy.
Tilghman: Don't have that one--any from Hyperion or Bis that might exhibit the sound? I might have some of those with chamber groups. This is interesting to me, I might go out and buy this disc (I'd like the music, anyway) just to hear what you're talking about.
I give my second vote to RCprince. I actually own a CD player with adjustable dither. I ran from the highest setting to the "no dither" setting. While the sound signature of the music changed slightly, there is no noticeable noise per se.

But on some chamber recordings there is a slight sound I would also attibute to the bows or something happening non musical with the instruments. I can also hear the clicking of the valves on the wind instruments.
I'm fairly certain the sound is inherent in the recording. It occurs immediately following a note from a "bowed" instrument, and is most noticeable in the quietest passages. The strength of the sound varies greatly from one recording to another, but is very common. I have never noticed the sound in any recording of "non-bowed" instruments. I would like to think the sound is generated by the instruments, but it does not quite resemble any sound I have noticed at a live performance. The idea of the sound being an artifact of "close miking" seems possible. I suppose I've become slightly fixated on the issue because I have spent so much effort , to no avail, tracking down the sound within my stereo. I think I'll bring a couple of CDs to my local HiFi shop to confirm that its not in my head...

Thanks to the group for the input...Tilghman
Well...a trip to the HiFi shop confirms that the sound is not in my system. The noise was apparent there, just like at home. The salesmen decided we were hearing the breathing of the musicians. I'm not so sure, but at least it's not my imagination.....
Congradulations Tilghman, you have good ears on a good system! What you are hearing is called Rosen noise. It is not a digital artifact, it is not anyone's breathing, it is not Brownian motion of air molecules, and most of all it is not all in your mind either. It is the noise of friction of bowhair bristles impregnated with Rosen against strings. On very revealing systems you can hear it. It is more prominent in softest passages from solo instruments or small ensambles. In a live performance you can hear it mostly up close to the performer, if acoustic propagation is exceptionally good, because it is very soft and decays rapidly with distance from the source. It may be slight more prominent with the larger members in the violin family. On occasion you may also hear simultaneously the noise of fabrick from the sleeves of the performer rubbing against the body of the instrument.
As a professional violinist, I'll add a couple things. The bow uses hair from the tail of a horse. This hair, especially when new, has microscopic barbs that hold the rosin. Rosining the bow enables the barbs to grab the string and the rest is obvious.

Depending on where the microphone is placed, string noise will be heard with some artists. Heifetz produced a lot of noise that could be heard in the front rows of the hall. This technique did produce an amazing, focused tone that soared over then entire orchestra and to the back of the hall. Heifetz got a bad rap for this, especially on many of his recordings. Those that heard him ‘live’ know/knew what an amazing violinist he was. I've been questioned for using this method at times in an opera orchestra, but ultimately I know something good and useful travels out of the pit. Fluffy playing is for the weak.
Its the artists and their clothing, or that's the trigger

only percussionist and the trombone players have to move as much as someone playing a bowed instrument.

What makes the sound strange is the gating and compression used in the recording to help reduce extraneous noises from creeping back onto the mics which could carry over onto oncoming parts of the performance and be even more distracting. Just shifting in the chair makes some noise that a mic will pick up. So gating is used and that's mostly what your're hearing.

At school we used to watch quartets in a church and the lite attendance for Friday evening concerts allowed us to sit right up front and the players clothing (especially men in tux/suits often made extra noise as did moving in their chairs.

All things you don't want on a recording.
I think this experience undelines some of the differences between live performances and recordings, especially if close micing is involved. If you listen to rock or jazz, think about how much more information you here when listening to an upright bass or drum kit through a high-end, high resolution system. Live sound and reproduced sound will probably always be to different, and potentially equally satisfying, experiences.