Hi mariadelbosque,
I may or may not have this issue as well. Truth is, I cannot hear very well, well, deaf, actually, without the use of aided devices. So, I really do not know.
BUT, I know of one trick I use when I do not want to hear something on my system or someone else nearby. I either turn the sound down, or remove my personal devices.
Until Avast! devs come up with a fix for this here, that would be the workaround I would use; as when Avast! automatically updates on a cold start-up, first connect, and then around four hours later (if using the free version), the same. At all other times, the system sound would remain on. As I do not use AIS, I cannot say how frequent the a/v updates are for that.
Manually updating the vps yourself will also prevent the *ding* *ding* from sounding as well.
No need to get aggravated unnecessarily here. I am sorry it is stressing you and other users out, but until then...