A couple of days ago I was just watching a video on youtube and I noticed that it froze and I kept hearing a clicking sound. I thought it was the video but it turned out that my whole system was unresponsive and the clicking was coming from the hard drive. I restarted my computer and everything ran perfectly, but I immediately re-backed up all of my important files. So far, I've only encountered a few problems like Safari hanging when it normally wouldn't but that's once in a blue moon. Is it possible that the hard drive is going bad or could it have been a one time glitch? At the moment I'm running techtool deluxe doing a surface scan, and so far nothing has come up. All the other tests that were preselected, my mac passed. Suggestions?