Finally...after weeks of being driven crazy by a faint, plastic-on-plastic sounding rattle, I found it! The sunroof (and/or the sunroof shade cover).

It always sounded to me like it was coming from the rear hatch area. I immediately did the felt discs on the rubber stoppers in the rear hatch - which did seem to help. I probably had that rattle also, but it wasn't completely cured. Still had that faint plastic buzzing/rattle sound.

Next I treated the rear seats with leather protectant. Didn't fix it.

Next I lubed all the door gaskets with Wurth rubber protectant (and about three or four other things). Nope.

Used lithium grease on rear hatch latch, door latches, rear seat latches...Nope.

Had my wife drive while I crawled around the back. Found a rattle in the left rear panel where the CD changer rack is located, a silver metal box at the floor level. Insulated that with foam tape. Still had the plastic rattle noise.

Damn Damn Damn.

Then....eureka. When I was in the back, the sound seemed like it was coming from the front of the car. Weird how sound travels like that. I isolated it -- by process of elimination - to the sunroof area. I put the sunscreen all the way back, raised the roof in the vent position, and put three small pieces of foam insulation tape where the trailing edge of the sunroof meets the car. Instant fix. Now that the rattle is gone, I'm terrified to touch the sunroof. I'm even leaving the sunscreen open in case that was rattling and not the actual sunroof glass panel.

Ahh, sweet silence.

I guess the moral of the story is, don't totally depend on your sense of hearing while you're driving to pinpoint the rattle or squeak. Have someone else drive while you probe and poke around for the rattle.