I finally found the solution!!

This irritated me so much I actually came back to all the forums and registered so that I could help other people fix this. (P.S. I never leave comments on these forums so you must know how much this stupid popup thing annoyed me that I actually come back and registered)

It is a malicious app that is causing it. In my case it was "MP3 Music Download Best". Someone else found it was "Simple Mp3 Downloader". It could be potentially be almost any app though.

The app that I used to find the malicious app is called "Ad Clean & Antivirus by StopBadApp Mobile Security". It has great reviews on Google Play as well.

Install this app and let it scan your device and it will find the app that is causing your problem.

Let me know if this sorts out your problem. This popup thing has been annoying me for weeks and I would like to know if this helped anyone else.

Good luck!