What's with ads showing up below search text boxes?

This has just started to show up, and it's particularly irritating. It's happened on sidereel.com and audible.com. You type a search term in a text box, and an ad shows up below the text box, usually totally unrelated to the search. Adblock hasn't caught up to this, but, boy, is it irritating in the meantime!

It's happening in Explorer and Chrome.