Booting into Android 'Safe Mode' will disable third-party apps that may be causing the issue.
Remove any dubious apps, apps obtained outside of Google Play Store, warez apps, screensaver apps, apps that allow watching movies for free or without paying, and other Ad-dominant apps.
From the first place, I would check which suspicious program came installed on the system; usually by uninstalling it will reduce the symptoms but recommend to scan for remnants.