Now I am sure it is a problem in my casio 5s pro. I reset the piano and reinstalled the new firmware. After about 10 minutes I start playing the piano I hear a sound that is not caused by pressing the keys. after this time the keys A, B, C, D (LA-SI-DO-RE) emit that strange sound that you can hear in the audio files I posted. After a certain period of time everything returns to normal and the keys emit their normal sound. Perhaps it is better to ask for the replacement of the electronic piano