Posted this a while back on the Apple discussion forums but got no real help. Hoping someone here can point me in the right direction. For the last couple of days my Mac Pro has been making this weird sound, not too loud, it sounds a bit like a hard drive spinning, in a rhythmical way. It's almost like it's breathing. It's one of those noises that once you start to hear it you can't not hear it. It's slightly intrusive as well as I do audio work and it can be picked up in the background. Would anyone have any idea what this might be? I haven't added any new hardware or software in the last few weeks, it's not a CD or DVD spinning in the drive, so I'm struggling to try and figure this out. Audio clip - http://leftback.info/mac.mp3 Any help much appreciated. Thanks.