GNU screen: C-A G ----disables audible bell.

I did not understand that visual bell is a 'feature'. I thought it was a bug. It was the only reason why I did not make a full use of GNU Screen. Now I know.
In xterm the default should be no visual bell. However, you can use `xterm +vb` to explicitely disable it.
In my case visual bell was enabled in /etc/screenrc.
What is interesting, is that any user changes behaviour of all users, of the whole system.