A rattle near the right door turned out to be the seat belt buckle banging against the seat. It would rattle only when driving over large bumps (So Calif has bad roads). I moved the buckle up and no more rattle. It took about 3 weeks to find it. My Porsche service could not find it and tighened the door latch.

 

I hate the darn seat belt buckle rattle. I move it up as well, but every time someone rides in the passenger seat the buckle gets pulled right back down to where it can rattle up against the door pillar.