I thought Middy picked up the same rattle in the right rear seat I've heard other owners complain about.
The real reason, at least in my case... The right rear seat belt buckle!
Just make sure it's aligned as shown in the picture and no rattle.
I had the opportunity to sit in the back seat of a Model 3 this weekend. The backseat is very low or the floor board is very high. I’m only 5’ 8”, but I felt like my knees were way to high compared to my seating position.
Honestly I loved virtually everything about the car except the back...