*shrug*... I use Avast, and get only ads for enhancements for their own services when they refresh. I just close them. Unless there is something I've missed, I don't think I've ever gotten that sort of behavior. I'd suspect that some other script/malware has gotten in. Avast is good, but not perfect, and there are problems out there that are not actually viruses, and are not in Avast's domain.

Have you tried Malwarebytes? or do you use any other ad blocker?