hi. i got my imac 27 core 2 duo base in the 4th of december. and then today was the first time this happened:
http://www.youtube.com/watch?v=Kf4rQlfHOYU
i started when i was working on an idvd project. it wouldn't stop. a restart solved it (it was about 20/30mins ago). i didn't happen again, and i'm working again in idvd so i guess it's not overheating gpu related. i have the lastest updates both software and firmware. if it happens again i will sound the alarm