I traced my excessive Disk usage to WmiPrvSE.exe
And as you can see, I've found a solution.
Open your Services program. The easiest way to find is just click Start, type Services, hit Enter.
Under Services (Local), scroll down until you find the “Windows Management Instrumentation” service and select Restart.
I have to respectfully disagree to this as a "solution".
avast is misbehaving, not playing well, bugged, incompatible, whatever you want to call it, with windows. Do we fix windows or avast? Even if we fix windows, do we do this every boot? This is bug that avast simply need to fix.
I too ran into the same problem, the activity seemed to either stopped on its own, or stopped after I tried several things found from searching the forums...