Is the hard knocker squarebill the new version of the rattling one or are they two dfferent models?

The original kvd square bill is silent. Later Strike King released a rattling version ( may have been a now exclusive but not sure). And within the last couple of years they released it in the Hard-Knock. So there are technically 3 sound variations to choose from. I believe the hard knock is not replacing the rattle version.

Yeah there's 3 versions. The Hard Knock is a good bait. I've been a big fan of knocker style baits the last few years vs the regular BB style rattles.