I have last years iMac 24 2.86. Recently, for the first time, I noticed the heat building up , in particular the top left of the unit. I had heard about heat problems but never bothered to check my iMac as it runs well. So, I downloaded iStat and notice that the temps seem pretty high, but not as high as some posters say would be alarming. What I find most interesting is that it has a temp for the Airport Card. I don't have one, as far as I know. What is that all about?