I'm not sure if I am missing something, but I haven't been able to change the sound played when something explodes.
In the vanilla ruleset, every explody thing has the same "hitSound: 0". Presumably OpenXCom uses a similar system based on the explosion's power to determine the noise, like the original?
I have tried to import new sounds in BATTLE.CAT, which works fine for firing sounds, but did not change anything for hit sounds. Or do you need to change a different file?
I've attached a flamethrower ripoff mod I had been working on a while ago, in case anyone wants to test things. It defines a hitSound and the appropriate entry for BATTLE.CAT, but every time the flame jet hits the ground, a small explosion sound is played instead of the flamey sound,