My new 'Cool & Quiet' system sounds like an aircraft waiting to take off ....
25cm case fan (on the side)
2 x 12cm in the back
1 x 12cm fan in the top
1 x 12cm intake fan in the front
not to mention PSU fan, CPU heatsink fan, 2 GPU fans and 3 hard discs whirring.
-Carol Haynes
9 fans!?

Your PC is suffering from the 'way too many fans' syndrome!
My P-IV 2.4 GHz (I heard new duo-core Pentiums don't get as hot) tower has a temp-controlled CPU fan, the power supply has a temp-controlled fan and there's a huge (and therefor
slow/quiet) additional temp-controlled fan, covering the back blowhole to suck the air out/through the case.
That's all!* Before *You see the RAID HDs in light-silencing, vibration-reducing containers and the power-supply in its original position; the holes in the back aren't closed yet:
* After *You see the power-supply now in a horizontal position, making place for the huge blowhole and silent-controlled fan; the HDs are now directly in the airflow, *perfect* for cooling:

You see how it looks from the back; note the special fan mounting to avoid vibrations:
