hard drive noise drives me insane. i went crazy a few months ago and bought all the 'quiet' kit i could afford. so, two samsung spinpoints (meant to be super quiet) and two raptor drives (quiet spinning but super loud clicking).
all well and good, but now after only about 7 months the samsung(s) have started making a very irritating high pitch noise - whenever they so choose to do so. fantastic.
so, all i can see is you can have the most silent machine in the world, fanless, water cooled, whatever. but what can you do about hard drive noise when the noise comes from inside the drive case - nothing.
only solution i can think of is to put the hard drives away from where you are sitting. you can't really put modern machines in a cupboard because of the heat they'll produce so it looks like it requires putting the machine in another room with cables running through the walls. absolutely ridiculous measures just to have a silent hard drive. and no, a hard drive case enclosure won't help - i've got those already and the high pitch noise easily escapes through them.
so use earplugs or background music - or maybe just go back to have noisy fans.
sorry, that's not really answering your question, i've just accepted that hard drives are swines. thankfully, only a few more years to go and hard drives will be obsolete.