Double beep tone on Note 9

[AaDi4]

Since last week I am experiencing double beep notifications tone on my Galaxy Note 9 however there was no on screen notification from any application. I have searched for solution on internet but still it's same no luck yet. Also dobe reset for all setting but still same. Wonder what wrong. Please can anyone help. 

[SalmanCh]

Just go into safe mode and check all recently installed apps, this must be caused by 3rd party app

[AaDi4]

safe mode I have tried it too but still same. btw in safe mode only limited apps are working.

[DrShahid]

Check in into notification settings

[AaDi4]

checked them all but still same!