Ok this sounds daft but I have an unusual problem. Every time I switch on my iMac, I get a noise like a rollercoaster in the background. I have disconnected all the peripherals and rebooted but it is still there when it boots back up. It drowns out any music or videos I try to watch. I have deleted the kids accounts in case it was something they but no luck. Picasa is switched off as is iPhoto, Photobooth, iDVD, Garageband and iMovie. I know this is going to be something stupid - something the kids have done maybe but does anyone know what is going on here? or is there a way I can determine what audio processes are runnning with a view to deleting them. I can see the processes via the utility but have no idea what might be relevant Otherwise, I assume I will have to re-install OSX. Any help or hints gratefully recieved.