What causes random clicking/navigation sound while PC is idle?

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?

It could be Spyware/Adware/Malware running in a background process. I haven't seen this for a few years but I remember seeing a hidden application called something like system32.exe in a windows folder location that just "loaded" adverts but not display (guessing to raise a pay per view account).

If I was you, I would do a scan of your system for general Malware, and take a look yourself using Microsoft/Sysinternals Process Explorer (an enhanced Task Manager) and AutoRuns (A enhanced MS config for viewing everything that starts up with your machine.

I had this problem and it drove me crazy. Turns out I had a search window open and xp's animated search dog was scratching himself. I swear it's not a joke. I turned off the animated character and it went away. Turning sounds off in the control panel will not fix it. You have to right click the dog and choose "Turn off animated Character"

Unfortunately it won't help you as you're on XP, but for people on Vista and above you can track down the source of strange noises by opening the volume control window. It has a volume slider (and mute button) per app that's running and flashes the one that's making noise at the time. I've used this in the past to track down a strange noise.