Hello, I have a two 20' ALU iMac's. One was bought in 2007 and one in 2008. Both are in the same office. The 2007 model gets really hot on the Alu casing on the top but the 2008 model does not. Using Istat the temps measured in the 2007 model were at least 10 degrees hotter than the 2008 model. Is this normal? And does it matter that it's hotter?