An interesting article from Silent PC review.

http://www.silentpcreview.com/modules.php?...rtid=121&page=1

I like that phrase.
QUOTE
This is the reason why Seagate states in one of their white papers that minimizing the difference in noise level between idle and seek for hard drives is psychoacoustically more significant than achieving the lowest idle loudness.


I suppose it means that we (or the brain) tend to ignore constant sounds more than varying ones.