Actually I see this as a potentially serious issue in terms of noise control.
I'm severely deaf and wear a hearing aid and I normally just turn my speakers off so I wouldn't know if there was a noise there. There's no indication that Avast is making a noise when the virus alert comes up.
So how would someone who can't hear at all know that this was going on unless someone complained, probably made him feel awful in the process (Yes I know and this does happen) and told him to switch it off? I can see occasions taking place when someone is using Avast on a home PC with speakers on, doesn't know the alarm makes a noise and irritates the neighbours no end with it! Very few programs make noises unless you tell them to.
The procedure needs to be a little more transparent in terms of visuals I think when the Avast warning takes place.