The 'Show last popup message' just shows an ad for avast! Mobile Security. This was no doubt piggy backed on to the update and I suspect that this may be what is screwing it up.
You could be on the right track. I never got any of these ads and never had a problem.
I've also had these ads on some systems. (these ads make the VPS updates happen). It could be the problem.
The ads don't make the VPS happen, they are piggy backed on to the VPS update, but they appear to cause a problem.
There were previously piggy backed on to the VPS update (avast
without this problem, whilst you only saw the ad/tip popup and not the update one, the voiceover did announce for the update. If you used the 'Show last popup message' option it showed the update popup and not the ad/tip one.
But something is messed up in avast 9 with the auto update notice and sounds.