This is my sistem an as you can see it's very similar to this
http://img106.imageshack.us/my.php?imag ... 125wx1.jpg
you can't here it all the time.
my fans now are
3 tricool at 5V and medium so the fans run at 3.5V, two on top and one in front of psu.
3 CM 13DB 700rpm at 350rpm (under motherboard regulation) very silent fans but no move air and very silent at very low speed, one on the first tower of ifx-14, one in front of graphic card to do an air-tunnel (it's the best position because the same fan directly in front of p182 it's for me too loud), and one on accelero S1 on my 8800gt AMP.
1 Noctua NF-S12-1200 with ulna at 600rpm and under motherboard regulation (about 300 rpm) on the second tower of IFX-14, very silent.
fan of enermax infiniti 650W no go over 650rpm.
but i've not finished yet!