Are you talking about analog tape hiss? Common from the early days of stereo (listen to any Mercury Living Presence record or CD and you'll hear it), and an "evil" of analog tape vs. digital tape (one of the aspects of digital recording that many felt enough of an improvement over analog to overlook the flaws of early digital). There are some programs available to eliminate that noise from a master tape; some remasterers try to eliminate it, others don't because they feel it compromises the high frequency content of the music.
Where does that hiss on the master come from?
I was recently listening to a remastered version of physical graffiti and I was amazed at the amount of noise it had on it - I mean its remastered! Then I listened to Aja which has absolutely no noise in the back. I asked a very knowledgable friend why the remastering couldn't get out all that noise and he said that the noise must be in the master. My question is how does noise get on the master? Thank You!