ok, so I found some info, it's some Stupid info and just is one more thing to add to Nvidia being stupid, cheap, and cutting corners. If you've purchased a New 9600GT, there's apparently a second edition of the Newest wave of 9600GT's and the 8800GT's that are the same, but different. they can't be adjusted. the Fan's only have 2 wires coming off them and into the cards board. those 2 are for power, and if there is a third wire, thats for speed control. Nvidia and many many company's that make the cards are only using the 2 wires and are not allowing fan changes. the fan should get louder during games when it's needed, and slower when it's not needed. if thats not happening then maybe its' a driver issue.
So basically how new is your 9600Gt, when did you buy it, what brand is it.
and if you don't mind opening your case, you don't even need to touch anything, but look and see how many wires are coming off of the fan. like it's main power wire should have 3 wires. or 2, if you see only 2 wires from the fan, then thats bad news.
let me know what you find out. Sorry man