Hi, I have the same OS and Avast version than this user and I'm experiencing something odd: at every boot, icons are being "rebuilt" (Programs menu, folder windows, they show blank for some seconds) and there's a crazy disk activity by Avast (checked in sys monitor) which lasts about 2 minutes. Also if I use the searchbox in Programs menu, I have to wait seconds for results to show up.
Needless to say, just some days ago the system was much snappier and I thought the latest Avast program update could be the reason.