This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
No idea what the reason might be, but you're not alone.
On the Apple iMac board, a user has reported that "During the [sleep light update] install your fans will run at full blast for about a minute. Then they will go back to normal and you will need to reboot again."