iPhone audio speaker distorts

HI, the speaker of my iphone 11 pro distorts, calling the assistance that sent my phone to the Czech Republic for 2 times not having any problems. I contact the service center in my city and after a quick diagnosis they tell me that there is no problem on the phone but the operator confirms the distortion.

I call Technical Support again and after having provided some videos that highlight the problem, they tell me that the problem is related to some frequencies but that they cannot continue.

Bad, really bad.

Have you had similar problems?