Open the case side door and turn on the PC - there are just 2 stand alone fans CPU and exhaust, and power supply. Tell us which is making noise. It is easy to get replacement for CPU fan even from newegg - there are a lot compatible products there, if it is exhaust fan, it is also very easy. Power supply will take a bit more time, but it is easy as well.
While you do this, you have opportunity to upgrade your Inspiron 570, are you interested? You can easily upgrade it to the level of current Inspiron 660 model by changing processors and increasing RAM, also, if you did not upgraded your VIdeo Card it is fairly easy to do.
Let me know if you are interested.