Alright, so this is only my fourth post here, but I thought I'd share what I'm currently running. I started work on this PC towards the beginning of the year, and it's come a long way since then. I was using a Toshiba laptop for a while as an all-around computer, but I mostly used it for the internet and as a music source. However, it was getting a bit slow, and I'd wanted to learn how to work with computers, so I decided to build a full-sized PC to play my music from. With a little help from my friends (and an abundance of cheap, used parts), I managed to put together a working computer. However, I wasn't quite happy with it, so it went through about three motherboards and numerous peripherals to get it to this point. Along the way, I ended up buying a Scythe Kabuto CPU heatsink to replace the stock one, and an 80mm Scythe S-Flex fan to replace the screaming ARX fans that came with the case.
After assembling it the last time, I realized I was getting some hum from the S-Flex fan, and thought that dampening the case might help. I did a google search on sound-dampening materials, and managed to come across this site, and the rest (as they say) is history.
ASUS P5GDC Deluxe motherboard with Intel P4 3.2GHz CPU, cooled by a Scythe Kabuto heatsink and 120mm Noctua NF-S12B FLX fan, controlled by three-way voltage switch. Ram is two sticks of no-name 1GB DDR.
ASUS GeForce EN8500GT video card, cooled by an Arctic Cooling Accelero S1 heatsink.
ASUS PCI-G31 wireless-G network card. (It's not brand loyalty, it's cheap and common parts.)
Maxtor DiamondMax 10 (I believe) 80GB PATA HDD running Ubuntu 10.04.
Generic 460W PSU wrapped in aluminium insulation (because of its proximity to the CPU) with 80mm Scythe Kama-Flow 2 fan, controlled by a Zalman Fanmate.
Aluminium, rack-mount, horizontal server case with rear 80mm Scythe S-Flex intake fan on a Zalman Fanmate, and front 120mm Nexus Real Silent exhaust fan hardwired to 7V. There is also a custom top being made for the case, and the bottom and rear panels have been lined with 1/4" cork (for sound deadening, although I'm not sure if it helped much... I wanted roofing materials, but the smell threw me off, and I couldn't find heavy rubber). In case you're wondering about the placement of the intake/exhaust fans: Due to the arrangement of my furniture, the back of the case faces my seating position, so I reversed the airflow through the case to reduce turbulant noise.
LG DVD combo drive (barely used) and NZXT touchscreen fan controller (which is currently unhooked, more on that later).
And now, because this thread is useless without pics:
The front of the case... there had originally been a "door" covering the entire center part, but it's been removed. The gap for the floppy drive and upper drive bay have been covered with electrical tape. The middle bay contains the fan controller, and the bottom is the optical drive. The green you see on top is the protective film on a sheet of acrylic.
The internals of the computer... The Noctua fan on the CPU heatsink is clearly visible, and below it you can see the heatsink for the GPU. A little harder to make out is the silver insulation on the PSU, just at the top left of the picture, behind the Noctua. The upper right is the cage for the optical drives.
Last pic, this time from the back. Here you can see how close the PSU and CPU heatsink actually are. You can also see the HDD towards the front of the case, on the right. It sits directly over the Nexus.
All in all, it's relatively quiet... I've got a bit of turbulent noise, as well as some hum which appears to emanate from the Noctua, possibly due to case vibrations. I've also got HDD noise, but I'll be isolating that this week. Other than that, I'm going to cut a hole in the acrylic sheet directly over the CPU, converting the Noctua into a combination intake/CPU fan and eliminating the rear fan. I also need a fresh air duct for the PSU, although I'm debating between drawing cool air in from the optical bays or from the top of the case.
Anyway, this has been a long post, so my thanks to whoever gets this far into it, and my thanks especially to Mike Chin and Co for the site and the knowledge on it... I'd probably still be trying to figure out the source of my noise if it wasn't for this site, let alone getting this far.