That seems more like your typical adware type thing.
First suspicions would be any app installed within the last week or so.
It would be easier a while back, because apps that have ads used to show them soon after install and use.
Now, many apps wait a certain amout of time before they begin showing ads.
Check out the apps that you recently installed, and clear the caches of all of them.
Ads are usually stored in the cache of apps.
If you can narrow it fown to which app the ads came from, you can uninstall it.
Before you do, be sure to clear all data of the app before you uninstall it.
Some apps will place their ads in a different area, and they will remsin and contiue after the app is uninstalled.
Deleteing all data before uninstallation helps to prevent this.
IMO apps that do either of these things desearve no place on my device.
If you 'just can't live without' an ad-filled app, then you have some options as well.
https://f-droid.org/en/packages/net.kollnig.missioncontrol.fdroid/
https://f-droid.org/en/packages/org.blokada.fem.fdroid/
