I saw a post on another forum that sparked an interesting though-process for myself. Can which-clauses such as the one I am about to show example for be considered adverbial? The reason I ask is that I have always known these relative-pronoun led clauses to be adjectival clauses.

My son chews with his mouth open, which aggravates me.

Seemingly, "which aggravates me" applies to the main clause completely. So is it functioning adverbially? I could also see how one could say that the which-clause is taking about the action of "my son" chewing "with his mouth open", but then again, if we let that presumption call for an adjectival designation, I believe a lot more brick-and-mortar adverb clauses could be adjective.