Sharp Beep occurs at Random after Android 7.0 Update

[Jay Pr]

I have an AT&T Nexus 6 and updated to Android 7.0 in late November. Right after the update a very sharp beep will occur at random throughout the day when the sound is on. I've gone through all app notifications, found nothing and I'm thinking it's from the system. The build number is NBD91J.

 

[Tim1954]

Look in settings.... Accessibility.... Notification reminders..... You may have some persistent notification turned on.