nubsub, I had that rattle near the head rest area. It made a 'tick 'tick noise when I went over any imperfection in the road. I noticed that when I drove with the car door not fully closed but latched (I don't suggest people to do so), the noise went away. To make the noise go away, I tweaked the upper door frame ever so slightly inwards and the noise went away (knock on wood). Don't know if that is the same noise as yours, but it sounds like it.