Everything in Mac was designed for silence, but there are 2-3 ugly culprits that rob the efforts in Vain.
IF you got the lottery crap end of the stick you will own
Sony dvd drive (loudest device in the computer I Have ever owned!) Other random pick is Pioneer. There is no excuse to be this noisy, the drive reeks!
Seagate HDD. The newer device by Seagate does not mirror its past accomplishments, it trades places to the once slightly noisy WESTERN DIGITAL (other builder pick). IT likes to make a lot of crackling sounds when seeking, it won't be a bother unless you like to defrag in windows a lot (fat32 gets fragmented a lot quite to my dismay). But in MAC osx, the drive won't seek too much except for loading data before game saves or other similar things.
If you did a BTO, the noisy x1900xt fan is a vacuum cleaner. Its not as loud as the dvd drive, but still combined with all these problems you start ripping out hair.
A. I ordered a samsung drive, known for silence. I hope it will work.
B. Nothing is done about the seagate
C. X1900 xt was upgraded with Accelero X2 fan, now this kitten is quiet!
No ramping up and down during games or rendering
Always the same speed, and always good reported temperatures about 15-20 c quieter !