Noisy Demon trunk lid?

If it is actually the trunk lid inner liner hitting the outer steel sheet causing this noises you suspect, you would likely be able to feel/hear the movement of it by you simply pressing down on the lid after being closed. If there is excess movement causing noise, likely causes are bad seal, or incorrectly installed springs, hinges, latch issues, or trunk misalignment. Nonetheless you could begin checking by simply temporarily placing a few clean soft wash towels between the lid and trunk opening perimeter. This should generally rule out trunk lid movement caused noises and you would avoid all the work of actually removing the lid like you mention doing.

Also, this is not an idea for many/nowadays, but here is something we would do in the old days to quickly/easily figuring this out would be to find a volunteer to jump in the trunk while taking her out for a quick spin. They could listen to identify the cause in person. In modern times you can put a GoPro camera in the trunk, and or alternatively remove rear seat back with liner, and bring someone along to do some observing from cabin passenger seat while you drive. Good luck.