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.
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.