The screw is loose and I've tried tightening it, but seems I need to get behind the body panel to access nut or whatever is back there, but there does not seem to be an easy access. The panel is therefore squeaking and/or tapping as I drive.
Rear side panel screw nearest tire loose. on 2005 Scion xA
You may have to bite the bullet and remove what you must to gain access. It isn't always easy to do some things on a vehicle even though it seems very minor.