I tried blue and red o-rings on my MX Blue and Black keyboards--the ping persisted.
I removed the o-rings and 'stuffed' the boards with shelf liner, then tried an old yoga mat, even some sound-dampening material used in cars--no joy, the ping never subsided. It did diminish somewhat with the shelf liner and other sound-deadening materials, but it was still loud enough to be annoying, I got rid of CM and Filco keyboards.
The only MX keyboard (I still own) that doesn't ping is a Corsair K65 with MX Red switches. But Reds are a bit too light for me, so I hardly use the Corsair.
I'm all Realforce/55g Topre (2x) these days; they're quiet out-of-the-box, zero ping, and they 55g Topre switches have superb feel.
If a reasonably priced, stock, no-ping MX Clear keyboard is released, it will be my next purchase. Until then, no more CM, Filco, or KUL keyboards for me. I've not owned a WASD, but ping pandemic has escaped WASDs keyboards. And let's not forget CM and Filco's unwarranted price increases--same keyboards-->increased profit. As a consumer, 'Enough".