I have 3 120mm 30dba fan's in my computer running, they are quiet.
The only time I can even notice them is in a completely quiet room, which they aren't annoying in the least, I just can hear them.
Unless you wan't a completely silent computer or 3dba more is an incredible difference 33dba should be plenty quiet for just about anyone except someone who wants a silent PC.
E6300 w/ Arctic Freezer Pro 7 @ 3.6ghz 1.4Vcore
Antec 900 Case
EVGA 750i FTW Mobo
4x1GB of G.skill DDR2-800
2 8800GT in SLI
22" Samsung Syncmaster
1 250GB WD and 1 Seagate 7200.10 in RAID 0
Corsair 520HX 3DMark06 Score: 13900