When I use the RMBP on a table or my lap it makes creaking noises. Upon further examination, I noticed that the back cover screws were loose and there was plenty of flex due to this. I went to a local AASP, since it's always a pain to get into the genius bar. He tightened it up and most of the creaking is gone. However, there it still creaks a little bit when I place my hands down on the "palm rest areas." Has anyone else noticed this problem? If so, is there a lot of flex around the back cover screws?