I have always had MBP, but this week I bought my mom a macbook and I have been setting it all day. i shut it down and then closed the lid and then for the hell of it opened the lid again and noticed this crack sound. I repeated opening and closing a few times and it is defiantly making a sound only when opening not closing. It seems to be coming from back left area, but no damage is noticeable. is this normal or should i be taking it in to an apple store?