On my Dell D630 laptop running Windows XP Pro SP3, I randomly hear the "Windows Navigation Start.wav" played. This happens even if the only application active on the PC at the time is Microsoft Outlook and no one is touching the keyboard or touchpad. The start navigation sound IS enabled for Internet Explorer (I have IE 7 installed), but it is not running (no window open, anyway).

The clicks are rapid, as if being executed automatically by a script or process, and they always come in threes: "click-click, click". I don't see any changes on the display and I don't know how to figure out what's running that could cause this. I have tried to leave Windows Task Manager open in the hope that I'll see a process name jump to the top of the list briefly, but it doesn't happen that often and I guess I'm not quick enough. The PC is slower than I think it should be, but System Idle Process is at 96 - 99 during the event, and for most of the time when I'm not actually using the machine. Any ideas?