Token2Shell/MD plays a WAV sound file when it encounters a CTRL+G (BEL; 0x07) ASCII control character. A bell icon is also displayed on the title bar at the same time.
If you want to change the sound it plays, the option is found in [ Tools ] » [ Settings ] » "terminal" » "ASCII BELL (CTRL+G) sound".
If you select "<none>" for the sound, Token2Shell/MD will not play any sound and the visual bell will also be disabled. If you want to just keep the visual bell, select any sound other than "<none>" and set the volume to zero.
If you want to add your own WAV sound files, it's simple and straightforward since Token2Shell/MD gets the list of sound files from its Home Folder.
In order to add your own sound files, first change the Home Folder to any folder you can easily access. You can change the Home Folder from [ Tools ] » [ Settings ] » "general" » "home folder".
Launch File Explorer and go to the newly selected Home Folder. Under this folder you should find a subfolder named "sound"; copy your own WAV sound files to this folder. That's it! Newly added sound files will be automatically listed when you go to the sound options.