Turns out, the GBA crash sound is just the console playing its entire address space as sound data. If we have a clear recording, we can convert it back to actual bytes, thus dumping the RAM and ROM.
Used source code is available at: https://github.com/zzazzdzz/zzazzdzz....
Note - this is hardly a ready-to-use solution, and requires a lot of tuning, depending on the source data format.