The fan in my Coolermaster V8 recently turned its toes up. It had been noisy for a while. It was still keeping my overclocked i7 920 cool at idle, but I daren't play games with it failing.
Yesterday I did something insane - I put a Jetflo in. The CPU is now, at idle, running 12°C cooler...
It's not what you would call silent though...