Send your phone to Apple, they replaced mine (Europe) cause this is a massive quality control issue, if you check the forums it has been reported previously. I even checked the store models, all had the same problem, from normal Iphone 15 to the Max Pro.
Test your phone with this song https://youtu.be/G5xSLbYMr-I?si=r0U_wDIhrG39ZlIi 1st 10 seconds it will rattle like crazy.
I'll get the phone back in the evening and I'll meet you know as soon as possible.
Had to wait for almost a month for the speaker repair part to arrive.
Some proof from the Estonian authorized Apple store seller (Valge Klaar)
https://preview.redd.it/32siih5ac32c1.jpeg?width=1080&format=pjpg&auto=webp&s=d6676f97025c70ae93568bf7fc6aa0c10b7b813b