Why am I getting a notification sound every 4 minutes when there is no notification?

[AC Question]

I have checked all the settings. It even vibrates when in silent mode, so have to power off at night!

 

[the tall guy]

Hi, try resetting your phone into safe mode - https://support.t-mobile.com/docs/DOC-5744

does the problem still persist in safe mode? if it doesn't continue then a 3rd party app that you have downloaded is causing the issue. Start by removing the apps one by one until the issue is resolved.