Tech heads: What is a common mechanical fault in desktop PCs?

the loud whirring will have been your PC's fans working overtime. by this i don't mean anything technical... i just mean that your PC was most probably overheating due to hardware failure/error and your fans have had to work harder to cool the components. i suggests that you run the PC (providing that it still works) with the side of the case off. check if the fans are running okay. if they're okay, give the inside a little clean out to get rid of dust. PLEASE DO NOT CLEAN THE INSIDE OF THE PC WHEN IT IS TURNED ON. it's just not a good idea. if it's not the fans or the dust, i can't help you. sorry.