I’m accustomed to update checks slowing things down a bit (less for me, on broadband) … back when I was on dialup, from frequently checking process explorer it appeared that the primary slowdown was while avast.setup was running through the list of servers to find an available one. Once it succeeded in connecting with one, that was pretty much the end of the slowdown, whether or not it actually found an update to download.

And I do seem to remember that in antique versions there was a separate icon showing that an update was in progress, although that only seemed to appear after a successful connection and therefore not showing during the worst of the slowdown. Or am I thinking of the icon for the now mercifully retired VRDB?