I know you can turn it off, after opera has installed its update but isn't about time opera stopped doing it. The noise is worse than an air raid siren going off outside your house, never mind in your house.
So, please please please drop it from your updates. Its really annoying and if my little un falls asleep downstairs its going to wake him up because you never know when an update changes the settings because even if you turn it off, its only off for 1 or 2 updates depending on what they are. You don't find out until you open opera and that oh so annoying noise comes on. Its a noise...if it had been a few notes of music without making full use of the speakers, It wouldnt be so bad.