It seems to me that your PC is storing lots of data, from your gaming activities, across lots of locations on your hard drive. Initially there's very little need for your PC to access the drive but, as time goes by, it reaches a point where the Pc is constantly trying to access different locations on the drive at very high speed. So the normal quiet clicking sound (which can be heard whenever a drive is being accessed) turns into a constant buzz.
Chris
PS: Good evening, Chuck. I've driven through your area twice today. With the Woolpack offering bitter at £1.69 per pint, I'm surprised that you're not down the pub!