That is a strange fan that's on a 92mm mounting pattern but is a larger diameter blade than you'd find in a normal 90mm fan. I just looked at mine and it looks like any 92mm fan (called 90 for convenience just as 119mm fans are called 120 for convenience) would fit. 92 mm fans aren't that numerous out in the channel (only one page of them at jab-tech) - not sure I've even noticed a PWM one in my browsing on our ATer approved fan sites..
Why not try a manual fan controller on it to see if you can cut the noise enough while maintaining good cooling - or your mobo should be able to control both normal and PWM fans, just you only get a few speeds with a normal fan. Or just do some searching with your favorite engine. If you've been keeping your eyes open here at all, you know where to go for fans. Looks like a 92 to 120 - found the Scythe Kama 92mm PWM out there, but it's a normal size 92 mm fan. Looks like the Scythe Kaze Jyu 100mm low or med. speed fans might work too (give your current blade size w/o the noise) - check out the large pic at jab-tech.com . He has several normal 92mm size with PWM there as well. The Panaflo 92mm low or medium speed are noted as being quiet.
ThermalFX has the 92x32mm SanyoDenki normal 3-pin - up to 55 CFM. And Sidewindercomputers usually has a page of 92mm - the Delta 3-blade is nice but currently OOS.
Newegg has about two pages of them but quite a few are OOS at the moment and their ship cost is high for a singleton. This Silverstone is very like the stock fan on the TX2, but even more CFM (thus probably even louder unless dialed back - and OOS for the mo):
http://www.newegg.com/Product/...x?Item=N82E16835220016 - it's OOS too.
I wish CM would pop for function over looks on their HSF fans...
.bh.