I don't know what the problem is. Some fans in my computer are going nuts. They whirr up, run high for awhile, and then go down to half, then go off, then whirr up again. Usually this thing is silent. I'm showing over 99% of my system free in activity monitor, as it should be, I'm only running Firefox. Mac Pro 2.66, 5 Gigs ram, 10.4.11. No software updates available. any ideas?