I was in iTunes when I heard a slight grinding sound form the speaker area and I thought nothing of it. About 5 minutes later I was watching a youtube video and the grinding got louder to the point where I could no longer hear the video. I immediately powered the iMac down and upon reboot process, the grinding sound could be heard again. After the booting process, the sound is gone. I am wondering what it was and if I should waste my time taking it in to an Apple Repair Shop