Any ideas what this is? It rattled out from behind the passenger-side mirror when I shut the door.

 

LOL so I'm not the only one... My 2013 was less than a day old and I had same issue but my driver side mirror. I took it to the dealer and they didn't know what it was. Told me to hold on to it and if I had any issues they would replace the mirror under warranty. I just had it replaced 2 months ago because the mirror was making a vibration noise. It still worked but the noise bugged me.

 

In case you want to disassemble the mirror for inspection...

https://www.jk-forum.com/forums/modi...-panel-320560/

 

Have you tried to adjust your mirror since then?

 

@red2010rubi I did move it, and it seemed to move like the driver's side. I'll report back if it rattles or falls off.