I just tightened 7 of the 10 screw on the bottom of the mac.. Some required a 1/4 turn... I've never opened it before so it came like that out of the box... For now, it seems the creaks went away...
i wouldn't doubt it....my powerbook was creaky till i retightened all its screws again, no creaks now (except for the screen, bc i cant get to ONE screw )