Loose screw inside deck?

Hi all I just received my deck last week and hadn’t used it much yet but there seemed to be a loose screw in the top right of the deck that was rattling around inside and driving me mad.

I followed a guide to remove the back and got the screw out, small black one about 4mm in length, I could not see any missing screws inside so I sealed it back up and everything’s working fine. Anyone else had a screw loose inside and anyone got an idea where it might have come from? I’m just hoping it’s not a fan screw or something that would normally not be visible