NOTE: This has only been tested on the WINDOWS version of Mythruna!
We're all most certainly awed by the bass-y glory of the menu buttons... in the sense that they probably caused your subwoofer to nearly burst into flames... but it's not the most palatable sound when all you want is some peace and quiet, since the options currently don't let you turn down the volume on it. Worry not, though, for it can be changed in a few, simple steps!
1. Access Mythruna's game folder; it should contain the folders "lib" and "mythruna.db" along with the executable, some logs if you've played a few times, and some .dll files.
2. Enter the "lib" folder.
3. Using Winrar, 7Zip, or some similar application, open the "assets.jar" file.
4. When you're in the assets.jar file, enter the sounds folder.
5. In the sounds folder, you want to replace "boom.wav" with a similarly named and formatted sound file. DO NOT simply remove the sound file or use just any wav file you find. That'll break your game.
I modified the boom to be much quieter in a sound editor. You can download that sound
here. It's just a heavily modified version of the original, but it's way more forgiving.