I was workin in the ofifce and one of the macs that wasn't being used all of a sudden started making a loud noise. No activity on the comp whatsoever. the case was vibrating thats how loud the noise was. I shut it down quickly opened it to see if any cables some how came into contact with a fan. I moved some cables around and nothing. Still happens. LOUD AS HECK. I don't have MDD g4 its a later one than that. Any ideas?