FWIW flat wound springs are a common fix for that noise w/AR buffers. Not sure of a source for a flat wound CZ97 recoil spring though.
I dropped a DPM recoil system in my CZ P-07 Duty years ago, that was a flat wound spring in a captured setup, similar to the setup in my Walther PPS. A nice upgrade from the polymer guide rod but about $75 so not cheap. DPM website doesn't show if the CZ97 setup is a flatwound spring.