SPCR is a great site and a great resource but perspective is very important.
For me, I like my system very quiet. With the ambient room noise, you can't tell if it is on or off. At night, you can't tell either unless you put your ear right up to it.
For some of the SPCR hard core people, my system would be completely unacceptable. It is not Quiet PC Review, it is SILENT PC REVIEW. Over the years, some people on there have gone to incredible lengths to achieve total silence - oil immersion, encasing hard drives in acrylic, etc.
On the road to silent, the first 90% is not that difficult and just requires some knowledge, planning and a moderate premium on things like nice fans and a good PS.
The last 10% of that journey will take all your time, money and sanity (IMO).
This. As Zap said, the best reply in the thread.
I started at SPCR many years ago after purchasing my first PC from a builder. It sounded like a leaf blower. After carefully sifting through info on SPCR, I chose my components and built my first PC, and it was very quiet. That's where it all began.
As david noted, the first 90% is just doing some reading, planning, and forking out for parts you think are grossly overpriced. Then you get your start and it's great.... for a week or two.
What follows is that you then start to notice all the little annoying sounds that parts make which were previously unknown to you because fan whoosh covered them up. That's when insanity begins.
After about 3 years of building SPCR inspired PC's, I've come to a point where I'll gladly hear the calm whoosh of a fan over hard drive vibration or coil whine. SSD's come in handy here, but once you start on the road to utter silence, be ready for the challenges and frustration that can lie ahead. My advice? Build yourself a good PC with slightly audible fans, a good thermally controlled PSU and spend the small amount of money it takes to pad all the moving parts like HDD's to reduce vibration.
Best advice I ever took from SPCR: Use zipties and vacuum hose from an auto parts store to mount your fans. The hose acts as a vibration dampener, and the lack of a solid metal screw helps even more. Sure it doesn't look super sexy in the case, but it might cost you 2-3 bucks for a whole case and works a hell of a lot better functionally than fan gaskets and expensive silicon grommets.