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Damn, this is the sound I strive for.
It may be that you're used to the sound of foamed boards so having a non-foam board sounds too loud to you. >

That does sound harsh and clacky, yes, but not unpleasant. I've heard others sound pretty similar, and I've heard others sounding quite muted, so you'd need to look at some sound tests on YouTube and see what they list in their build details.  Maybe they did something different? Foam between plate and PCB perhaps? No foam at all tends to let a board sing a little louder.  Personally I don't mind it. >

It’ll probably get louder and clackier with GMK caps. Adding one or two of the foams might help tame it a bit. >

I love that clacky sound. A tape mod behind the PCB would filter away the high tones.