Not sure about your preference, but I prefer to enjoy PC creativity away from vacuum cleaner type of noises... That's exactly how my PC sounded, before I put an end to it. Here's how:
i) First, I removed and cleaned the big heatsink from the microprocessor. It contains a noisy, tiny fan. To reduce the noise of this fan one needs to reduce its speed by by about 15-20%, by inserting a low Ohm resistor in series with its power supply.

ii) Next, I removed the big power supply box and its noisy fan, reduced its heights, by removing its cover and cutting down (using tin snips) its sides until almost even with the highest part in this box. Mine went slim to less than 2 inches! Caution: To protect against accidentally touching its parts I covered it with plastic grill. The whole box I then attached outside to the back of the PC so, that the opening of the power supply faces the PC' inside.

iii) Into the empty space, previouly occupied by the power supply, I position a 7.5 inch or 18cm (in diameter) fan, made from a used cassette recorder motor and thin aluminum blades (from old persiana blades) glued onto the plastic capstan.
I left the PC without its metal cover and covered it with a colored, decorative curtain, instead.
Result:
The PC stays cool and now is almost inaudible! Even the hard drives etc. benefit from the big, quite fan. Albeit the fan moves about 3 times as much air, due to its size and low velocity it generates no noise. Small fans are noisy, because they have to run fast in order to move the same air mass. I "stole" this idea from observing a household cooler fan...
I'm enjoying this arrangement already for almost 2 years now. I'm not sure though, if this arrangement is suitable for a faster, more powerful system, but it certainly works with my lousy 1GHz Pentium PC. If you like to see pictures of it I can send some.

 

Very interesting! It begs the question, are you trading off noise for cooling power? Reducing speed of fan, definitely will reduce it's effect. Secondly, internalizing the power supply's fan, definitely will make cooling more daunting for the PC.

My friend, who is equally crazy about PCs and audio, does a lot to try to cool his system while keeping it quiet. In the end, he ran waterblocks through out the system (processor, GPUs) to a radiator. He has a very high quality fan that pushes the air directly to the outside via a dry conduit. During the winter, his 8800GTs and processor do not go past 30d C. It is also an extremely quiet computer.

Steve

 

Pretty weird, my PC only doesn't make much noise after boot-up. Sometimes when I need to blow the dust off the fans. Haven't done much to it, except added a gig of RAM. 2002, HP Pavilion 524w, a cheap walmart special...

 

Very interesting! It begs the question, are you trading off noise for cooling power? Reducing speed of fan, definitely will reduce it's effect. Secondly, internalizing the power supply's fan, definitely will make cooling more daunting for the PC. My friend, who is equally crazy...
Steve

Sorry, that I'm not yet as crazy as your friend... but you missed my message. I mentioned "I left the PC without its metal cover" thus, there's little of "internalizing the fan" going on. The effect is as when one would open the PC and put a running fan in front of it! The fan blows cold air into the PC and pushes warm air out of the PC! What more you want?!

Here's a Pic of it: http://img2.freeimagehosting.net/uploads/0d1aa4046e.jpg

As a musician I very much appreciate a cool and silent PC...

 

hi jjj,

i've been exacting my way of silencing my pc too lately, your post inspires me more.
what i've been planning (but not yet done, not enough urge yet ) is like this:

i'll remove every fans there is from the unit.

the processor's will be replaced by a fanless big size heatsink with the same heat resistance as the original one using full speed fan (i figured it would be less than 0.2w/°c, and maybe about 10 x 20 x 5 cm in size), and it sould be protruding to the outside of the casing.

the power supply unit will be without fan too, and the same will be done with all of it's transistors, sharing one large heatsink about 10 x 10 x 5 cm in size also out in the open.

the harddisk will be covered with a soundproof material 2cm thick, and the flat side will be stuck on a 7 x 10 x 5 cm heatsink.

i'm not using any video cards using fans or watercoolers.

this system will be almost noiseless and is perfect for audiophile music reproduction

 

The flat side of the disk is very thin and won´t do much help for heatsinking. You should use the two sides where srews should go. There even exist heatsinks for disks that are mounted this way.

 

that's a good information for me. thx kubeek