Hi all, I've got a real puzzler of a problem and I'm hoping you can help! I have a 24" Intel iMac, with the latest version of Snow Leopard. I bought it last July and have AppleCare. For as long as I can remember I have this problem with it: * Every 30 seconds, almost to the second, the audio from the built in speakers distorts and gets slightly louder. This lasts about half a second then goes back to normal * It only manifests through the internal speakers, it's fine through headphones * Rebooting makes it go away temporarily * I've reset PRAM and SMC to no avail * I've tried turning Time Machine off to no avail * I've taken it into my local Apple Service Centre, they couldn't replicate the problem, it only seems to happen in my house (every room I've tried it in is the same) * I bought an expensive power filter/conditioner, this hasn't helped at all I'm at my wits end with it! Please can one of you clever folk give me some suggestions? Thanks!