Remonster

Noise is my ultimate enemy when it comes to my computers. To date I have built 5 complete silent PCs, that is 5 separate computers with noise as a major concern, none of these PCs has had any of its performance sacrificed in order to achieve minimal noise. My latest creation is in my Antec P180B, it is so quiet that I could comfortably say it is the quietest 4GHz+ system on Overclock.net :) but with no way to prove that I guess that is nothing more than an empty claim. Anyways, I've decided to share some tips and tricks for silencing your PC without reducing performance or getting much higher temps, most of these are standard fare for people like me who frequent PC silencing forums and who look to kill every last bit of noise from our PCs, but a few of these tricks are things I have come up with over the years by simply thinking of a new idea, trying it and if it works posting about it here or on SPCR (SilentPCReview).

I will organize this into categories based on each individual component of the PC:
Case: Firstly you want to choose a case that has very good airflow, 120mm or larger fans are definitely prefered but do not get anything with any fans smaller than 80mm. The larger the fan the more air it can move while rotating at a lower RPM, and with all other factors equal, lower RPM = lower noise. The minimum number of fans you'd want in a high heat output machine is 1 120mm intake and 1 120mm exhaust like the configuration found on the Thermaltake Soprano, with the intake up front at the bottom and the exhaust at the top of the rear panel under where your PSU would be in a normal ATX case. This is effective because cool air falls and hot air rises (convection) the lower intake takes advantage of naturally cooler air in your room, blows it into your case over your hard drives and into the motherboard area, the air rises up as it gets warmer and the higher exhaust is able to exhaust the hottest air in your case first.
Fans: Choosing fans requires looking at a number of specs of the fans themselves, dBA (decibels) are a measure of a component's noise output. The higher the dBA rating the louder it is, but there's a catch. The dBA scale goes up exponentially meaning that every 10dBA you go up, the noise is roughly doubled so a 20dBA fan is half as loud as a 30dBA fan. The next most important thing is CFM (Cubic Feet per Minute) this refers to how much air the fan moves, the higher the CFM the more air the fan can move thereby keeping your case cooler. Do not get any case fans with more than 100CFM (50 is plenty) and I would consider 25dBA the maximum for anything I would put into my case but I'm a silent PC nut so 30dBA and under are fine for most people. Bear in mind that the dBA ratings of fans (when they aren't completely falsified) are taken inside an anechoic chamber (meaning a silent box, basically lol) there are a number of things that can reduce a fan's airflow and increase its noise, things like wire fan grills or even air filters will make a fan a lot louder than it would be on its own so I never use any of these, be careful not to get your fingers caught in a high flow fan because it will hurt! And also manage your cables to keep them away from all fans, if a wire gets sucked into a fan and is rubbing against the fan blades it will cause a loud buzzing sound which can drive you nuts.
CPU: If you're using air cooling be sure to choose a low noise HSF (HeatSink-Fan) like the Tt Big Typhoon, or any of Zalman's CNPS line (Computer Noise Prevention System) or if you choose something like the Thermalright Ultra120, be sure to choose a silent fan using the above guidelines.
GPU: I chose to use a 7900GTX because it comes with a very quiet stock cooler, but if you're card is louder than you'd like get yourself a Zalman VF900cu or similar silent cooler.
HDDs: Hard drives make a lot of noise, most of this noise is caused by vibrations from the actual motor spinning around at 5400/7200/10000/15000RPM. One way to reduce this noise is to simply decouple the HDD(s) from your case because when that HDD vibrates and is screwed directly to your case those vibrations travel through the screws right the the case itself causing the panels of the case to resonate and amplify this noise. Simple methods of decoupling HDDs include using soft silicone grommets to go between the HDD and the case so the vibrations are drastically reduced, more extreme measures include custom made harnesses that suspend the HDD in the case, but since I have never done this I won't go over it in any detail except to say that I've seen it done with string or rubber bands or even zip ties.
Optical Drives: Many people forget about these but in a silent system your optical drive can easily be the loudest component for the same reasons as the HDD, spinning a CD or DVD at the super-fast speeds found in modern optical drives simply is not quiet, use the same methods to decouple your optical drives as explained in the HDD section, some cases like the Antec P180 have a padded front panel that really helps cut down on the noise that makes it to my ears from my DVD drive which is nice, also some optical drives are naturally louder than others so you may want to pay attention to reviews you may read.
PSU: First and foremost choose a silent PSU, my favorite being the Seasonic S12 but the PC Power and Cooling Silencers are very good also. Once you have a quiet PSU you want to decouple it from your case by using silicone grommets over the 4 holes that you will use to screw the PSU to your case, a lot of people also forget that PSU fans cause vibration and that will travel right through the PSU to your case.

Now that you have chosen a full complement of silent parts its time to go one step further, using rubber or silicone fan screw replacements (like the ones found in this kit which I really reccomend: http://xoxide.com/nexus-pc-vibration-kit.html ) or silicone fan silencers on all your case fans will cut down on the vibrations I talked about earlier and can make a huge difference. Further silence can be achieved by undervolting your fans to 7v or even 5v using a volt mod (not reccomended as it can damage your PSU) or by getting a simple fan controller, my Antec P180's case fans come with build in L/M/H speed controllers so I am not using a fan controller but this is what I used with my NZXT Nemesis Elite: http://xoxide.com/subl4poblred.html for just over $10 it is really nifty.

Modding: If you've got a dremel handy and aren't afraid to cut up your case I just did this relatively simple mod to my P180B and it really helped alot, after doing all the things mentioned above the only noise emanating from my case was a faint wooshing noise which was the air from the fans being disturbed by the case's built in fan grills, so I cut them all out and I highly reccomend you all do so too, see attached pics.

If you have any other questions or suggestions feel free to PM me as I am always happy to help out fellow PC silencers :)

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jigglylizard

Great guide just when I'm buying a new rig that I want to run as silently as possible :D

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Remonster

I just got my P180B and I edited the FAQ to reflect a new method I just found out about, cutting away the fan grills to reduce wind noise from your fans.

slick2k5

nice guide, bro try using rubber c-linings to cover sharp edges on ur case where u cut the fan grills..:)