There is no "fix" that's how it works and what the sounds were recorded as.
I've considered making custom boards as a side project using Arduino and off the shelf MP3 players, and then you could customize like crazy.
It's possible someone modified yours, but again, not knowing what was done, it's near impossible to "fix".
Post a video of the problem (or audio) but again, without cracking it open, it's not like there is a switch for singing voices to be off.
Video of what others sound like https://www.youtube.com/watch?v=BBJwOCM0UG0
I purposely modified my McDonalds to reduce the volume of the music (easy enough, it plays when the motor is moving the vehicle) and returns full volume when the ordering window and pickup window dialogs happen (the car is stopped). I cheated and used a relay and a resistor in series with the speaker that is triggered by the vehicle movement motor.
In theory, someone could use an external MP3 board and trigger events from the various switches or motor movement- all while retaining the original board.