I'm not a linux expert. And I'm afraid to have problems about Wireless, wired or sound issue because of a system update.
So, I wonder how to stop
AppCenter update notifications?
I've overcome this issue by adding a custom command to the startup:
System Settings -> Applications -> Startup -> 'plus sign' ->
And it lives still. I just put it to sleep (silence). With this way
AppCenter works only if I open it on Applications menu!