I don't know if any of you might want to try this, but I'm posting here just in case. I used to have a C5Z and after I installed a foam insert that separated the front part of the car from the trunk area, the car was much quieter. Not Lexus quiet, but noticeably quieter. Now I have a C6Z and there was no way to put in a similar foam divider, since it's a hatch design instead of the fixed roof coupe of the C5Z. I guess I could have stuck a foam divider in, but then I'd lose my rear view mirror, and that was a no-go for me. So what I came up with is a 1/4" Plexiglas divider that also make my car noticeably quieter than without it. To make it as noise blocking as possible, I put a 1/4" wide rubber U-channel around the upper part that contacts the plastic of the hatch hoop. I made the pattern by using a piece of cardboard that's 1/2 the width of the hoop opening, and doing a check/cut./check/cut routine until I was happy with the fitment. The bottom of the plexiglass fits right up against the ~3" wide ridge behind the seats, and I then forced the upper half into the hoop area, and the rubber edging has kept it in place now for going on 2 weeks, with no sign that it's moving.

BTW, I installed it vertically at first, but the reflections from the front of the car was making it too difficult to see when using the rear-view mirror at night. Basically, the car headlights and any other lights would show a reflection on the plexiglass such that using the rear-view was just too difficult.

The rubber edging and pushed into the hoop area.

Bottom of plexiglass that sits in the carpet channel behind the ~3 wide ledge behind seats

Pattern made from cardboard

 

Yours is interesting, but this is what I did to separate the front from the rear hatch. The noise from the wheels and under the hatch area is trapped in the void made by the 2 partitions.


Both are made out of solid foam board covered with matching ebony carpet. still room under the hatch glass (top) partition to stow the removable roof.

 

That's very nice!

One thing I forgot to mention is that because the area is split into the passenger area and the storage area, the A/C drops the temperature much faster, and even the factory speakers can really put out the bass. On my way home from work yesterday, it was 111 F, and in the 30 minutes it took to get home, the temperature in the cabin actually got too cold, and I had to turn it up a few degrees! That simply never happened before putting in the divider. However, it also means the hatch area effectively doesn't get any A/C cooling, so it gets hot back there.