I had some squeaking issues with the rear hatch door plastic covers. The dealer put felt tape on the underside of the plastic to prevent the plastic from "squeaking" against the metal hatch (lower hatch piece). Perhaps you could try this. If it is a vibrating issue and the panel is loose you may need to replace the panel and the plastic clips that hold the panel into the door.

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2013 BMW X6M-current
2013 Audi S4-current
2007 BMW X5 4.8i (E70)-sold