An indoor unit that rattles may have loose panels, debris, or a failing fan assembly

https://floridaacservice182.talesignal.com/posts/what-to-do-when-your-ac-is-not-working-in-winter-haven

An indoor unit that rattles may have loose panels, debris, or a failing fan assembly. Turn it off and tighten only visible loose screws if it is safe to do so.