My Norco 4020 was also way too loud for my home theater rack, thus pimped mine too:
Figured it might be worth $12 for each of the 3 XLF 140mm fans since they claim <16dB. Simply epoxied them together, with a strip of aluminum across the top. Two strips of wood, held in place with screws through the case side, to keep the fan assembly in place.
I also built a mini thermostat to control the fans. See the variable resistor sticking through the front of my case. Honestly, there is no sound from these fans on, so the thermostat is simply to save a some watts of power when the system doesn't need the fans.