Perhaps try something with no metal plate inside, e.g. aluminium plate. Acrylic plate or plate-less can even be better to reduce the ping. Also, add some padding / foam underneath the PCB to eliminate empty space.
I was offended by the ping of some older IBM keyboards, and couldn't get use to the handsome Model M13, and eventually went for a rubber dome (IBM KPD-8923), and I'm now still partially a rubber dome person (HHKB with its plate-less Topre domes). I've also converted to linear also, but on a Noppoo 84 Choc-mini there's the steel mounting plate, so even my Gateron blacks with o-rings (to reduce key travel) 'ping', with less echos than the Model Ms in such a smaller 75% case. I kind of like it.