I have been having the same issue, was playing a game and Avast decided to be rude, and minimize my game and popup the Smart Scan window.. Had me scrambling to close the blasted window, so could get back into the game before what I was doing in game got messed up.. After I did a repair not sure if it fixed it, but I did turn off Silent mode option and so far it has been behaving.. So I am thinking that Silent mode is broken..
Well it seems that even after repairing and what not, the problem is still happening and it is getting to the point of being really infuriating..