iPhone 15 Pro: the speaker makes the case and frame annoying vibrate!

Hi,

my iPhone 15 pro produced in December 2023 when I watch videos or listen to music (tik tok, youtube, iTunes Store, AppleTV...) emits a sound vibration from the speaker that mainly affects the back and the frame.

I feel the vibration between my fingers and it increases when I turn up the volume. It's annoying, ruining the listening experience.

I did a test at Apple Store and the speaker was ok, but the problem remains.

I also tried it without the cover (original Apple) but I didn't notice much difference.

Is it normal or is a defect?

​​Thanks