Hello! We're happy to announce that we just pushed an update which makes it possible to turn the mismatch sound on and off. Please look for the option in the Settings screen.
You will also see another setting which only plays custom sounds when matches are made. This setting doesn't affect Cubistry since Cubistry plays the Istrys default selection sound when selecting a single cube but for other Istrys this setting will make it so selecting a cube will play the default Istrys selection sound then play the mismatch sound if mismatch sounds are on. If mismatch sounds are off and custom sounds always is chosen then selecting a cube will play the custom cube selection sounds even if a mismatch is made. We will be rolling this out to all currently released Istrys on Steam shortly. Enjoy! ːsteamhappyː
Sincerely,
Hohng LLC.