Had the clunks and pings. All better now.
Used
Dupont Multi-Use Teflon Lube.
Applied to the accessible areas of the rear tray from the trunk. Didn't remove panels or pry things apart.
The spray lube has a fast penetrating carrier that dries quickly and isn't sticky.
No more crash and bang in the back. If it ever comes back, it's a quick fix with no damage.