audible rattles are hard things touching hard things.
simply put soft things between the hard things.
it's really that simple.
some examples of soft things are
* felt, fleece, or other fabrics
* weatherstripping foam (closed or open cell)
* rubber strips (neoprene)
laying deadener on a rear deck won't stop rattles. but gluing a sheet of felt between the various layers can. felt is cheaper as well.
the third brake light is a common rattle against the glass. weatherstripping foam does well here.
latches rattle. electrical tape around the latch loop will last for a few months. after it wears through, remove and replace.
latches include trunk, hood, and rear seat.
dome lights rattle - foam weatherstripping or felt helps here.
license plates rattle - closed cell foam weatherstripping is key here.
most cars have a pressure release valve with a flap located in the rear quarter panel. this will audibly flap with bass. you can remove it and seal it up with a piece of deadener or anything else rigid.
you can remove all of the interior trim pieces and simply line them with a thin felt. 3M Super 77 is a good spray adhesive. just make sure to clean them first for good adhesion. upon reassembly, you will have soft between hard all over. this is really just necessary at contact points.
you can see what i've done to cut down rattles in a car:
http://www.caraudio.com/forums/car-audio-build-logs-cars-trucks-suvs/516096-2005-scion-tc-sq-hertz-audison-pioneer-build-log.html