Hi, I want to share this story with you. I was updating my OS X to the new Yosemite and this is what happened. While it was updating, something that looked like smoke, puffed from both sides of the iMac. It kind of scared me, but the iMac didn't burn down and the updating kept going. I realized that it was just dust that the fan blew. Now my iMac has the new OSX and is running just fine. Anything like this happened to you?