Safari randomly opening new windows

Greetings,

I have searched the forum on similar topics, and have tried all the advice I found. However, I have still not solved my problem. I have a MacBook Pro from 2012.

My web browser, Safari, keeps opening new browser windows randomly. These include "scam" webpages for MacKeeper, Media Downloader, Car Insurance, Flash Player and various "warnings" about virus infections. The windows pop up frequently and without warning, even when I am doing something as simple as reading a news website or searching Google. (They are not pop ups that are tied to a specific website.)

I couldn't find anything in the Extensions tab in Safari Preferences. I removed various folders from my Library, as directed by other articles, and ran a scan of my laptop using Malwarebytes. (Nothing found.) I ran a scan with Etre Check but it did not reveal any relevant information. The problem still persists.

Any thoughts or suggestions would be most welcome. Most of the articles I read on this issues were from 2013 and 2014.