I've been noticing this "crunch" when bottoming out Zilents - especially on modifier keys where I have to hold the switch down.
It's there on all the variations of Zilents that I've tried so far, but I don't have the same thing with MX Silent stems.
I'm assuming it's the little rubber bits on the stem giving way under load.
Now that I've picked up on the feeling it's hard to ignore - totally harshing my chill with Zilents.