Is your rear license plate rattling when you close your trunk/hatch or when you are just driving down the road? There is a fairly simple fix to prevent that annoying rattle.
The main cause of the noise is the license plate frame is not being held close enough to the license plate, allowing both to rattle against each other. One way of eliminating this is to apply a couple strips of automotive sealer along the top and bottom of the license plate holder. The sealer will pad the frame and get rid of that annoying rattle.