What the others have said applies and will get you what you want, however the GBA has several shortcuts which may apply.
If you want GBA sound then while GBAtek will get you there I much prefer to linkhttp://belogic.com/gba/
(navigation at the top).
Many GBA games use the sappy sound format, there are a few more devs doing their own thing compared to the DS' sdat format but it is a good first port of call.http://www.romhacking.net/documents/462/
There are also several utilities to handle it.
While you can consider essentially every NES, MS, Megadrive/genesis and SNES game to use a custom audio setup from the ground up that you would have to pull apart it is always worth trying sappy first on the GBA.
Once there you can set volumes to zero, loop the track (pokemon hackers are fond of looping and have several guides to it) before it plays a note (or make a silent note and loop that), break the samples it uses so nothing technically plays and probably a few other things you can do other than fiddling with assembly calls.
Offhand I am not sure about the GBA wave samples formats and what might be used here (it is not as nice as the DS, and the DS has such capabilities sort of in hardware and in many SDAT games). That said if the music is sappy then whatever handles that will likely also be handling the voice samples and thus you have a very nice jumping off point (set a break on read for anything that bothers the music, watch it back and forth to find where it calls the voice and stop that from happening).
There are some checksums on the GBA but they are mostly for the header which you won't be bothering. Outside of possibly some anti piracy and some anti intro removal none apply beyond that and that is not what is happening here.