i tried a few simple remedies: Blanket in the frunk, and a a thick one doubled up under the new Tasmanian truck liner.
I honestly think it made a small difference. The main issue is clearly from the wheel wells though and the strange openings above the cubby holes - if you put your head next to the slits/openings and tap on the outside of the car or above the wheels themselves, it's like a drum resonating right into the car.
That said, it seems like some good sound deadening there and completely sealing in that section could make a huge difference. I'm looking for local body shops willing to do it, as that's beyond my DYI time and skills. I'll report back when I make some progress.
The strange openings above the cubby holes are for condensation evaporation. Most vehicles that have rear hatches that I have owned have some type of opening/venting like this.
However, I am very much in agreement with the majority of the noise coming from this area. From Monro's tear-down videos, it is clear that Tesla cut corners insulating the rear. My BMW X5 has a great deal of strategically-placed insulation in these cavities, including both solid and soft foam pieces. Our MYs have two foam cubes ("Teslaracts") lazily placed in the cavity. Nowhere near enough to control sound. I have a high-quality, adhesive sound-deadening kit that I purchased from Eastwood that I never used, so I'm going to pull out the rear carpet and side panels and cover the rear. I'm confident that this will make a huge difference, because when I pull back one of the side panels (they easily snap apart at the top), it is all bare-metal in there.