I've recently given my rig another thorough clean inside with a gentle brushing, especially to all the fan blades, followed by a careful compressed air blast to clear out the residue. Now it is back to running as quiet as when new. TC.
I'd looked at QuietPC as I always try to buy from them first. The problem with their modular silent PSUs is that they're only silent at idle. When you put them under load the fans can spin up to 30db or more. If you work through the specs you can see the claimed noise ranges vary quite a bit. The fanless ones aren't modular.
The Xilence range 'looks' good but the fan on mine has got noisy and 135mm quiet fans are nowhere to be found. I did try to source one from QuietPC. The Xilence claimed cfm and db ratings are a bit 'iffy' too.
PC Specialist ( click here ) pride themselves on their attention to reducing noise, and that's one of the reasons I ordered a desktop PC from them in April 2008. Wish I hadn't.
The PC was fairly quiet, but I had all sorts of problems, and sent it back with 5 recorded faults in 2 days. It was returned to me with 4 of the fault symptoms still present, and effectively unusable for internet access. I sent it back and asked for a full refund, which they agreed to without hassle. Basically I have no confidence at all in their ability to diagnose faults and carry out adequate testing.