Quoting Craig Sanders (cas@taz.net.au):
as Rick said, server manufacturers typically don't bother optimising for low fan noise because most customers don't care - the servers will be going into a noisy server room anyway.
What was disillusioning about that is that high-noise fans are also _low-lifetime_ fans: Fans that are noisy because they are built on cheap sleeve bearings are likely to seize up within a few years, at which point they provide no cooling, only more heat, thus possibly setting off a heat-buildup cascade that substantively destroys the unit. It was depressing to contemplate that my one-time employer had saved mere pennies on fans and thereby endangered the product's service life. What was more depressing was that this bad practice is routine in the computer hardware industry -- and not just in servers, but particularly there.