My Asus desktop PC is making a dreadful clunking sound like banging empty pipes down below on a boat every few hours.

No pop ups and I checked with Lavalys Everest for errors in sensors but nothing.

I'm pretty clueless with stuff like this , so would appreciate some help on what to do.

Windows XP pro SP2 with FireFox .

The only sympton of performance degradation is Firefox.exe in Task Manager is reaching enormous levels in virtual memory > 700,000.

Don't know where to look, or what to look for.

Sorry for such a boring thread, might make a century if CMn, Keda and Benbaa chip in with some help