I setup my new iMac today and everything seemed fine. There were multiple software updates, one, which included a firmware (iMac only) update for power nap. After the updates installed and the computer went through a few restarts, I logged into my user account. Now, I can slightly (though quite noticeable) hear the fans running. There wasn't any noticeable sounds from the iMac's fans till after this update. Does anyone know what it could be or experiencing the same thing? Edit: After the updates, when I shut down the computer, it also locks up for a second then shuts off. More specifically, the animations freeze, like the dock dropping off the screen. This isn't a clean install. I migrated from a Time Machine backup and then updated to Mavericks from ML. If a clean install is suggested I may just do that. Edit 2: Clean install took care of the freezing on shut down. Unfortunately the SMC update caused my fan to be audible and obviously a clean install didn't do a thing. I also tried resetting the PRAM and SMC to no avail. Here's some information on Apples website: http://support.apple.com/kb/DL1699 Please contact Apple regarding this issue so that it can get taken care of.