App notification sounds aloud when phone on silent and no notification

[Eragon626]

Since the last update this phone has been sounding allowed the notification bell sound (without an app appearing in the notification bar) even when the phone is on silent and with headphones in.

I originally thought the occurrence of the sound was random however it occurs at the specific times: 3:24 am, 5:30 am, 13:00 pm, 17:00pm, 22:30pm.

So far I have done the following:

1) Soft reset multiple times 

2) Cleared the cash partition

3) left the phone in safe mode at those times and the app bell sound does not happen. 

4) restet phone settings 

5) restet app permission

6) set notification sounds to silent in SIM 1 and SIM 2 

The sound still plays outloud (I'm guessing using the media volume) even though I have rest everything, the phone is on slight, no not disturb mode, and even with headphones. At those times without fail the notification sound happens but no notification light or notification appears in the notification bar. 

[Pugs1957]

Hi, as you do not have issues in safe mode the problem is a third party app. Firstly install the Toast Notification app and see if it picks up where the notifications are coming from so you can uninstall the problem app.

[Charlie306]

On the app screen, press and hold the icon for which ever app it is, this brings up another menu, click the (i) in the top right corner which enters app information screen, click on notifications and set to silent.

[Ventor]

@Eragon626 ,Have you tried disabling NFC?

[Eragon626]

I've never turned NFC on, always been off

[Eragon626]

"(without an app appearing in the notification bar)"

[Eragon626]

Should I do this for both the main apps and those in the secure folder (i.e. download that app twice)?

[Pugs1957]

Good idea which may save some time.

[Eragon626]

No luck, notification bell still rang aloud but "toast source" and "nice catch" app didn't find it.

[AndrewL]

@Eragon626: Does an icon appear in the Status bar at the top of the screen when the notification sounds? Have you tried heading to Settings > Notifications > Recently Sent, to see if an app is listed here that corresponds with the alert?