I recently purchased a 2021 M3 performance. After about a month of driving I started to notice a loud squeak in my seatback. Like I'm sitting in an old leather recliner. I searched the forums and it seems like most of the discussions had to do with the seat base. My squeak was coming from the seat back.
I removed the plastic shell from the back of the seat, using what I learned on this forum, and had one of my kids sit up front and press back hard and jiggle left and right. I noticed the noise was coming from the top right of the seat where the metal rods that hold the plastic support enters the seat frame. I reached up and found that there was a plastic grommet that was free floating up there, no longer attached to the frame.
I pressed that guy back in and voila! No squeak!
View attachment 708961View attachment 708962View attachment 708963