unwanted snare rattle

my drummer has a nice old maple snare drum that sounds really good but it has a terrible rattle in it. we worked on it for an hour a few weeks ago and couldn't get it to stop. granted, neither of us know much about drums, but we'd sure like to save this drum if possible... any ideas?

what type of rattle? while he's playing or not?

Most snare rattle can be eliminated by completely detuning the bottom 4 snare lugs closest to the snare strainer. This sometimes changes your sound, however, so try this first:
Make sure the snare is not tuned too closely in pitch to any of the other toms - especially 10" and 12" toms. Hitting them will set off a sympathetic buzz easily if they are close in pitch. Each drum should be tuned to a frequency range all its own.
If other instruments are causing the buzz, then they need to be re-aimed or turned down. Again, make sure the snare is not tuned to the open notes of the bass guitar (E A D G ). A plexi screen will help a lot, if you can afford it.
Most of the time, snare buzz is not heard above the music, anyway.

well, the snares rattle with everything... but most notably with, well, the snare. like i said, it has a really nice sound but when it's hit the snares just rattle around so it doesn't get a really good crack. no matter how much we tighten or loosen the snares or the heads the rattle stays so we're thinking it might be an issue with the shell itself, whch would be a shame...

Okay, this is curious. . .
I've heard of drummers removing their lugs and filling them with stuff - cotton, tape, whatever, to stop lug rattle. Take the head off and make sure all of the lug screws are tightened to the shell first - before you resort to the stuffing-the-lugs thing. If there is an internal muffler, make sure that thing doesn't rattle as well.
Also, take the bottom head off and lay the drum flat on a table. There should be a slight recess at each side where the strainer is mounted; but the rest of the drum might possibly be out-of-round.
Are there stretched or distorted wires on the strainer? These would not pull tight even when the rest of the strainer is taut.
Check the string, wire, cable, whatever, that is holding the strainer in place. It can stretch and need to be retightened.
Is the snare-side head old? It could be stretched and distorted.
As far as getting a solid pop out of the snare, a lot of that comes from making sure everything - top head and strainer is tuned really, really tight. (Room for disagreement here among drummers) I have sometimes even put a battery or something similar in size between the wires holding the strainer and the shell, so when the I flip the tension lever, it pulls super-tight against that snare head. With bottom tension - besides the 4 detuned lugs, you just have to experiment with your individual drum. Again, as I said before, make sure your pitches don't match anything else on the kit or the bass.