Sorry to resurrect this thread, but this is the closest thing I found to what I'm experiencing now.
I went out on a meetup drive today in the New England area, and finished up my 1000 mile break in on the way. When I got within 50 miles of my destination, I realized I was getting what sounded like tapping noises from the rear of the car. It sounded like some plastic was loose and was tapping against sheet metal. Sometimes it sounded like rocks pinging the underside of the car when there weren't any on the road.
Throughout the drive I checked a bunch of parts near the metal of the trunk area, and checked to make sure the seats were locked. I couldn't find anything.
The weirdest thing was that I couldn't reliably reproduce the popping/banging noise: it didn't happen on every bump, it didn't happen on every turn, but it would happen at least every 2 minutes when driving normally around 45-60 mph.
I parked near the end of the day, opened the trunk, and used it to get some leverage to compress the rear suspension (figuring I might reproduce it that way). With the parking brake on, the suspension compressed as the car tried to roll forward, and the driver's rear quarter made this horrible creaking sound
Now if the car rolls a bit forward after I set the parking brake, it creaks as it settles.
So I think what I was hearing was the random binding/unbinding of some suspension piece in the rear of the car. The rear end has never made this sound before, and I don't think a car with 1300 miles on it should creak when the parking brake is set. Do you think I have enough to go to the dealer with this?