Intermittent crossed-out bell symbol
While using my iPad ( the iPad 3, even thought thats not the official name) I see a crossed-out bell symbol appearing and disappearing intermittently. What does this mean and why is it happening? Sometimes it appears with a volume symbol underneath the bell then immediately changes to the crossed-out bell and goes away after a couple seconds. Couldn't find anything in the iPad users manual about this symbol.
Thanks for your help in finding out what this means and how to correct it.
iPad, iOS 5.1