Why do calendar alerts sound when both notifications and sounds are set to vibrate only?

[iMore Question]

I have an iPhone 6 running iOS 9.3.2. I have always set my notifications and alerts for my calendar to vibrate. A week ago I randomly started receiving notifications and alerts as sounds. I have checked the notification settings under calendar and they are still set to vibrate. I have also checked the sound settings for the calendar and they are still set to vibrate. Does anyone know how to correct this problem? I like to see my alerts and notifications, but definitely do not want sound.

 

[Vinu Jacob]

Just wondering if you have a 3rd party App with a calendar function that is triggering for the same events.

 

[pkcable]

Perhaps Facebook?