So I just bought a 2015 Air last weekend and everythings been good since, except I've noticed that whenever I pick it up or set it down on something to use it, the casing creaks. I turned it on its side and noticed that the bottom cover/backplate has some give to it and pushes in slightly as though one of the screws is lose. Is this normal or should I go to the Apple Store to get it tightened? I've been reading about this on other sites and it seems people have the issue a lot with the rMBP and some people say tightening it is bad or it will just get lose again over time. Thanks!