There was an annoying low level hum coming from my case. I recently upgraded to a fanless motherboard, fanless graphics card and thought the old el-cheapo case fans were the culprit. I replaced them which helped somewhat but nowhere near as much as I’d hoped.
Enter this mod: http://www.silentpcreview.com/forums/viewtopic.php?t=8240
Simple, cheap and extremely effective. Not a common combination! You’ll need roughly 60cm per drive. Less than a pint of beer for a whole raid10 array!
