I have an Imac i purchased in 2006 with 2.16 GHz Intel Core Duo. I am not sure when I got it that it used to sound like there were fans working inside (however i'm not really sure that was the case). I do notice now that my mac does seem to get hot in the back. I'm pretty sure that this is not good so I shut it down when I'm not using it. What should I do now?