GH suggested I use shelf liner to dampen the ping in my CMQFR. I did it and it worked well; but I wanted a tad more dampening. So I added a second layer of shelf line on the base layer of the case except under the R1 space-bar row, there's too little headroom for adding a second layer under the space-bar row. The result is excellent. The keys, MX Blue, sound thocky and feel great. And the additional shelf line didn't prevent the case from closing properly. All it did was super dampen the CMQFR's interior. I'm sure many of you have done this, but I hadn't read anything about it, so I figured I'd post it.
After Pacifist's comment (below), I measured the thickness of the liner I used: 1/10" thick for a single layer.