I was using my 2012 27" iMac that is about 95 days old for normal work purposes when it emitted several extremely loud noises that sounded like a fire alarm. This persisted for several seconds, and I closed whatever applications I was running (MS Word, Safari), and the noise stopped. The computer did not freeze or give any visual error or clue. I checked the log files, and there were several created around the same time, but I don't know what to make sense of any of them. It seems to be working fine now. Is this a signal of impending doom/failure? I believe it made three long fire alarm like blasts, and then was silent. Note that the audio on the computer was turned all the way down, so this was not errant noise from some website or anything like that.