I saw a very old post about a rattle on the passenger side of the car. I have the same problem and found the source so I decided to contribute to the knowledge center of the forums (I have been taking a lot lately and now I can give back!).

Problem:
Plastic sounding rattle from the passenger seat area. Sounds like it is coming from the passenger door.

Source:
The rattling is coming from the passenger seat fore/aft adjustment handle. The handle has slop in the seat attachment pivot point. This rattles and causes the plastic trim on the seat to vibrate. When I hold the handle, the sounds stops.

Solution:
Not sure. I need to find out how to insert some kind of bushing between the hole on the handle and the shaft on the seat or add a spring to preload the joint.

 

i'll have to check that out bc i have some sort or rattle coming from the passenger side too

 

ive decided im just going to go thru my car and tighten down any things that look like they might come loose. im not a fan of rattles.

 

This ^^^