OK, so i woke up this morning and woke up my 2007 aluminum imac, and first thing i noticed was a strange loud noise from the fans, i thought "oh maybe some tiny dust particle got stuck or something, so I opened smc fan control and took it up to 2100 rpm, but it only made the sound even more annoying. So i left it on default, and after 5 minutes it seemed to be gone, but now every now and then, randomly, the fans sound like they increase rpm and the annoying sound comes back and then goes away together with the fans. So I don't know what is it. oh btw I put my head over the heat exhaust and the sound or bad fan seems to be the one that cools the optical disk. Any thoughts as to how why or what?