I use a PC fan for cooling, and it needs to be at full power to cool my box off, but the air wooshing noise is definitely there. How do you guys deal with that noise?
Most either minimize it as best they can, or try and cover it up, or both. You can try a muffler (probably not the best for a PC fan because of static pressure) or put sound deadening material where the noise is coming from (like in the utility compartment of a NGB box). You could also use a fan that makes less sound per CFM. The bigger the fan, the slower it's running, the better. If you use the 120mm fans, it is best to use the 120x120x38mm variety (as opposed to the 120x120x25mm). They work much better in static pressure environments, and can be run slower.
Most PC hardware enthusiats and overclockers will recommend Scythe brand, and so do I. They make 3 different 120x38mm fans. I used thier 120x38 3000RPM fan hooked up to a Zalman Fan Mate 2 for my rubbermaid. It pushes a ton of air, and you can turn it down with the twist of a knob till it is as quiet as need be, but still keeps your setup cool.
The other option is covering it up. Some put an aquarium on top of their cabinets. A PC next to your grow is a good way to cover up the grow's PC fan.