It's an app you installed! There is no bloatware installed by Samsung nor your carrier that will cause this. Search around the web and these all of Android Central for confirmation.
Checking apps with what? A rogue app is not going to be in plain sight. The best is to do factory reset. Wiping cache and storage, reset permissions, MalwareBytes or other tool.
The fault can lie with adserver, with a web site even.
Above is correct. But it's worth it. It does so much more than just block ads. You can firewall apps in the device so they can't access the internet and other useful stuff...