Every once in awhile my CPU fan will randomly start speeding up until it gets to about 2000RPM, the optical and hard drive fans will reach about 1250 RPM. After about 10 minutes of annoying fan noise it'll slow down back to around 1000 RPM for all fans. Is this normal? The temperatures all look fine according to iStat, and it's not like I'm doing heavy computing (just running firefox, uTorrent, and iTunes). Is there a way to regulate the fan speed, or do I possibly have a defective computer?