I have a 24" iMac which is just over 12 months old. I noticed recently that occasionally the iMac emits a short burst of grey noise, a sort of hissing which distorts whatever sound is being emitted at the time, (music or whatever). This happens at no particular time and when running no particular program. I have tested it with external speakers and also headphones to confirm that it is not the built in speakers that are causing the problem. The sound burst usually lasts just a couple of seconds. It is not particularly loud and is something I can live with. Anyone had this problem? Also recently the same machine has suffered from occasional kernel panics. Usually after being on for some time. Again at no particular time or process. If I restart the computer it often panics again. If I leave it off for a while it seems ok, I am wondering if this is some sort of heat issue.