I fixed the rattle package
I had to visit my dealership three times to fix the issue. Essentially, my 2016 HSE Lux had three sources of noise.
1) Squeaky sound in the trunk
2) Chirping sound in the rear passenger seat
3) Some rattles in the passenger-side B pillar
The 1st visit: The 1) was really obvious from the first day when I picked up my car from the dealership. When there are small bumps on the road, it makes squeaky sound every time. So I had to get it fixed. I was not very sure about 2) and 3) at those times honestly so I couldn't clarify the sources of 2) and 3). The dealership told me that put some kind of sponge or something in the tailgate panel. Plus, they lubed somewhere in the rear seat. It was quick fix (same day fix). But when I drove back to home, the same sound was still happening! In my garage, I tried to replicate it and I successfully reproduce the sound. When I pressed the left side of the tailgate, I was able to make the exactly same sound! I took a video.
The 2nd visit: I showed the video to the dealership and reproduced the sound by pressing the panel. Additionally, on the way to drive to the dealership, I realized 2) was not fixed at all. So I clarified 2) and 3) more. After a day later, they called me that they fixed 1) but couldn't fix 2) because they had to order a new part. Unfortunately, I had to get my car back half way done because I needed my car the next day. Since the mechanic took out some parts to fix 2), the noise 2) got worse actually LoL. It was obvious CHIRPING every time! The good thing was 1) was fully fixed anyway. They put more things in the panel, and they took out and put back the rear camera entirely to take care of that. The squeaky sounds is gone now!
The 3rd visit: Finally, the part arrived. It was another easy fix in the same day. 2) is fixed correctly. I don't hear any chirping sound from the rear seat anymore. Still I have some sort of 3) from time to time. But it is not that annoying and it comes on and off so I can't reproduce it easily. It sounds like the seatbelt buckle is hitting B pillar. It happens especially the entire vehicle vibrates when I fully press the accelerator. Anyway, if it is just by the seatbelt, I will just bear with it. I checked the mp3 that the UK forum posted, but mine sounds a little bit different. Plus, mine is not that consistent.
The bottom line is: you can definitely fix the tailgate noise and the rear seat noise for sure. If anyone needs more details, I can share what parts they replaced.