I keep hearing random sweeping noises... I cannot figure out what is causing them or what it is causing them... It looks like Safari is open, Ichat is open, iTunes is open, Preview is open, 2 pages documents are open and a keynote file is open... There doesn't appear to be any changes in anything when I hear it... I'm not receiving an im ... anyone have any ideas? I just heard it 2 or 3 more times while typing this.