One of the best ways to bring down the noise your system generates without switching to alternate cooling methods is to install a fan controller in your system so that you can control the speed your fans run at and slow them when you don't need the extra cooling.  Hardware Canucks finished a video review of two fan controllers from BitFenix, the basic five channel Hydra Pro and the Internet enabled, touch screen Recon which offers far more control than the analog Hydra Pro.  Neither controller costs more than $50, check out the review and see which would fit your system best.

"Fan controllers may not be a marquee item within many enthusiasts’ systems but the power they grant over airflow within a case cannot be underestimated. BitFenix's Hydra Pro and Recon controllers hail from very different ends of the spectrum but they both grant end users complete control over their system fans."

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CASES & COOLING