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...
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.