Well, if you don't have any case fans then your components will get hot and the fans on the CPU and GPU will rev up to deal with it. Anyway, I use a tower cooler so I can't really comment on the performance of the 955s stock cooler . If it's your GPU, then it should only rev up when playing games or something. You can manually set the fan speed so that it starts off cooler and thus doesn't have to rev to those rather loud levels.
What case do you have and how many fans do you have mounted to it. I would try running the comp with the side off and see if you still get the revving. If you do try to find out which component it is. If it is the cpus heat sink I would upgrade it. If you do not hear revving when the side is off then you need better air flow through the case.