I have a XFX 6600GT with the same problem. I corrected it by installing the Gainward Expertool and installing it. With it, I can manipulate how fast the fan spins and thus, how much noize it makes. Maybe its compatible with yours too.
Well, first of all, it's a beta. That doesn't have to say anything, but it may have some unexpected quircks.
I read it now natively supports 64-bits Linux installations. Maybe that can help with F@H.
Sorry to barge in like this, but I have to say I admire the dedication you guys have for "D" and dc'ing in general.
I am (well was, until I registered) a lurker at this forum for a while and crunch some for the Dutch Power Cows. If I wasn't in the subteam I'm part off for the past 5 years I...