Well, what kind of power supply are you using? Most of the time, when a card starts down-clocking itself during 3-d heavy applications, it's because of insufficient available power. Please post your PSU specs so we can check it out!
If you know it's not your PSU, you can try following this guide to disable the power save mode, and see if your games improve.
As to the noise, check to see if it's coming from the fan and not the actual board. If it is just the fan, then yes it's annoying, but not a killer issue or worth the RMA as long as you are getting the normal RPM's out of it. Could be that the fan bearing just didn't get enough oil in the sleeve when they built it. The fan seems to be working fine since you mentioned that you can adjust it through RivaTuner without problems. If the noises start getting worse, or fan performance starts dropping, then it's time to send it back.