You can hear them but when combined with my other 6 case fans, PSU fan, NB fan and CPU fan they are barely noticable. You can set Rivatuner to automatically adjust fan speed depending on temps or manually change it and when your gaming you either have headphones on or your speakers turned up so you won't hear them anyway.
I've been using a Rotel power amp and a pair of B & W floor standers so far, which has worked, to a fashion
. But this weekend I might have a go at fitting the VF900's from my old 7900GT's.