This was something I've been working on since the early 90's, having been a subject among serious audiophiles since long before that. It was around that time when I first went out and flipped all my breakers off to see if it really would make any difference. The improvement was huge, and being so easy for anyone to do its been my standard recommendation ever since.
There are many different kinds of noise. Its not all noise like the hiss you can hear at idle even when nothing is playing. That seems to be the noise the average guy complains about and does everything they can to get down to absolute zero. When in fact the worst kind of noise is the sort that gets interwoven right into the signal. It can be called smearing, it can be called grain, but whatever its called it does not belong and therefore its noise.