Samsung Note 5 keeps sounding notifications...CONSTANTLY! Even when I've enabled do not disturb

[AC Question]

I just recieved a warranty exchange on my note 5 due to the battery overheating then poof, it just wouldn't take a charge. My issue is I keep getting notification sounds, but nothing is showing up in my notifications bar. Its disturbing my and my husbands sleep. I have muted all email apps, facebook, twitter, ect... I even enabled Do Not Disturb, and customized it for important calls and alarms. But every 15 to 20 minutes the phone is still making a jingle and I can't even see where its coming from. The notification curtain is showing NOTHING, or Id know what app this is coming from and change the settings . Have you ever heard of this? Any help would be GREATLY APPRECIATED