i have a G5 dual 2ghz with 2gb of ram running osx 10.4.5.
today it exhibited some odd behavior. the fans started revving up and down quite loudly and you could see a red light through the grill on the front just above the power button. i'm assuming it's a light on the mother board. you can only see it because of the see through grill. a couple shutdowns and privilege repairs calmed it down but i'm concerned that it may be a symptom of something.