Small spaces make quiet cooling difficult. Bigger fans are quieter at moving the same amount of air. The more air you move over a given heat sink the better the cooling (with diminishing returns, see various HSF reviews). So go for something larger with good airflow and some very quiet fans.
My HTPC has a PSU with a fan that I've never heard since it's temperature controlled and I'm not abusing it. The HSF is a Scythe Ninja something or other with a Panasonic D12SL 120mm fan, can't hear it. Graphics card is an MSI N460GTZ Cyclone. Sounds like a loud card, right? Well it's dead silent on movies (good for those quiet scenes) and none of the games I play have "quiet" atmosphere so when it does get cranking I still can't hear it over the audio of the game. You can always get aftermarket coolers for real silence if that's where you want to spend your money. All that packed into an Antec Solo with a cheap 64GB SSD, although when I had the 320GB single platter spindle in there you couldn't hear it at all.