Just bought S4 yesterday. I read the manual (I am an engineer, yes a geek), have called Technical Support twice for other reasons. But all through the night, my phone now rings with my default ring tone every 15 minutes or so. I have no unretrieved voicemails or text messages. I have not set up any alarms. Does anyone know why this is happening and how to turn off?????????????? My phone is now in a drawer - driving me crazy. Lydia