I talked to Apple executive relations department via e-mail very briefly about this issue. I have a defect-free keyboard now, but it took a bit of effort and a search for the right tool.
It appears that there's a plastic "bubble" membrane that surrounds the actual keypress sensor beneath the key cap. I was able to procure a tool for detaching the problematic keys (a tiny plastic "spudger" tool that was made from soft plastic). It's critical to get the right tool, or you risk damage. I inserted the spudger at the interface between the case metal and the top of the key cap, and CAREFULLY detached the key cap from the top side so as to not damage the tiny hooks on the bottom half of the key cap. There are more-durable plastic "clasps" at the top of the key cap that snap in, but we're still talking about tiny parts, plastic, and small tolerances. Be very careful. Skill and luck are hard to separate in small sample sizes. Do not force anything.
However: by pressing on the plastic "bubble" membrane beneath the key cap, I was able to reproduce the exact "snapping" sound. Conjecture: either the keys were slightly misaligned so that the circular "presser" is making contact with the plastic membrane, or the curvature of the plastic"bubble membrane around the keypress sensor has a curvature that's just a bit off and it's making contact with the key cap in some way. Either/or.
Anyway, I used the same plastic "spudger" tool to apply gentle pressure to the plastic "bubble" surrounding the keypress sensor (likely changing the curvature just a bit), replaced the key cap (carefully sliding the bottom hooks in first, downward, then pressing gently on the top of the key), and the sound vanished. I was able to do this twice, with two different keys, with absolutely no damage to the keyboard whatsoever. It's held up.
Apple: I am completely willing to (at least attempt) to show you how to do this so you can issue a service bulletin and start performing these repairs in-store.