Hey guys, been following this thread for a while.
Found a fan which works GREAT, and also even dug through the crates at home depot to find screws which would easily screw onto the existing heatsink through the new fan.
I hope this saves you guys a lot of time. Note however, the fan is a 4 pin fan........so if you want to plug it into the Northbridge fan slot you'll need a 4 pin to 3 pin connector. I just plugged it into a 4 prong.
This fan has an RPM of 4300, and is only 19 DBA! It's also made by a GREAT company, Papst. My northbridge temps idle at 32-34 C and it's completely quiet!
I bought the fan for about 16 bucks here:
(NOTE: Remove the current fan, it's simple and temps are lower without leaving it in there.)
http://www.endpcnoise.com/cgi-bin/e/40mmpapst.html
If you want to purchase the same screws I used to mount it to the existing heatsink, here's all the info off the HomeDepot Screw Bag:
#4 x 5/8" Metal
Pan Head
Phillips
13 Pcs 24791
ZINC/CINC
Crown Bolt Inc
The Bar Code number on the back of the little bag is 30699 24791
Hope this helps everyone! Note, I'm using this fan with 2 eVGA 6800 Ultra cards. It's a very tight fit, but it pops right in. It baaaaarely bends a single fin on my EVGA heatsink, but it's not a problem at all. For those of you without hte gargantuan eVGA Ultra heatsinks even less of a worry.
Also, anyone out there who has a PC Power and Cooling 510 SLI PSU.......please note.........the fan in that thing is LOUD as well. I was super excited to remove the stock northbridge fan, only to be driven crazy by the PSU fan.
I was lucky enough to have an old PC with a PC Power and Cooling 510 ATX PSU which I found to be very quiet. I just swapped out the fan in that one and threw it in the SLI version.
For anyone who is driven batty by this same problem, just give PC Power and Cooling a call and ask to buy the same fan (NOT THE DELTA FAN!) in the "standard" 510 ATX PSU.
Good luck, and quiet SLI computing. :-D