For no apparent reason, and many times a day, my desktop emits an ugly "whoohsing" sound which I've been unable to identify. I don't find it anywhere in Windows sound files, nor can I associate it with any one program .Don't have to be doing anything at all at the keyboard in order for it to occur. Nor has it been identified by Avira or other virus program. It's such an unpleasant sound that I'm often driven to turn off my sound completely to get rid of it - not a good solution. Any help/clues would be very much appreciated.