Remember that some brands of laptop disk drive will make a rattling noise if you shake them

Yes, but that is a very delicate, subdued rattle -- sort of like what you would hear if you put a pebble about one millimeter in size into a heavy coffee mug and shook it gently.

If it is a heavy rattle, it is probably (as Rob S. suggested) the drive cage loose from the rubber shock supports; otherwise it is very probably (I would estimate 80% likelihood) a drive cable disconnected either from the drive or from the motherboard.

tanstaafl.