Bill Tindall
I would just head on over to Lowes or HD and get a caulk gun and a tube of silicone caulk of some color that blended OK with the wood. Put a small dab of silicone top center and bottom center and see if that cured the problem. The function of the silicone is to become a flexible nail. A little dab will do you. If it still rattles add two more dollops centered right and left. The silicone will be flexible enough to let the panel expand and contract as it wishes.