They're grumbling and mumbling on either to talk to you or not. It basically started when you three met on Garden of Eden. Crowley was tempting Eve, Aziraphale tried his best to cover his mistake. While you? You eventually got bored and decided to inspect Eden. And eventually became friends with these two.

Crowley: "I don't know... You ask them" Crowley grumbled in a frustrated tone

Aziraphale: "At least give me some things to say to them" Aziraphale protested back