Few ideas, thoughts, and suggestions that I have:
- The first way you could improve your cooling is by lowering the temperature of your room you could run your fans slower or even disable some. Thing is thermodynamically the hotter your room the less efficient ANY cooling scheme is. Think carnot efficiency here: ((temperature hot) - (temperature cold))/ (temperature hot) if the two temperatures are close together you get a small number over a big number, and low efficiency, thus more fans to do the same amount of work that could be done with a lower room temperature.
- Use 120mm fans, where possible, they are bigger and move more air with less RPMs and in turn less noise.
- Invest in a fan controller, if you have 5 fans I'll bet most of the time you don't need all that air moving power, when you're not pushing your computer to the max you can run the fans at about half speed, which should cut the noise by more than half. I personally do this and with my fans at 50% I notice 2-4 degrees more on average. This is a small price to pay for my sanity from the dreaded fans.