My 2.66ghz MacPro (2007), on occasion hear a wincing noise coming from the top rear of the machine. sounds like almost like HDD spin a very kind of whispery spin (not the seeking sound) almost more a spinning sound similar to a case fan. im just alittle nervous because my surge protector was accidentally shut off a few weeks ago while my system was on and i ran Hardware tests to test any of the hardware and it has remained up and running since then. im wondering if this a normal sound, its not a consistant noise/sound but i hear it ever so often. any info/advice would be appreciated! thanks!