I have a 2.4 Ghz Intel Core 2 Duo Unibody MacBook. Lately I have had shutdowns at no more than 75 C and fans at 5500 rpm (using SMC Fan control) and battery at 30% or greater. It is a sudden shutdown. Granted the fans keep going for a while on Skype but this is not hot enough for a thermal shutdown. What is this? Please advise.