On Showdown, Clangorous Soul does not cost any health to be used. Here is an example of that happening:
https://replay.pokemonshowdown.com/gen8ou-1017062059
The player should not have been able to get boost after taking Obstagoon's Facade, but the Kommo-o still got the boosts anyway.
He also asks if Soundproof is supposed to block Clangorous Soul from being used because he tried to use Clangorous Soul on his own Kommo-o. I believe this to be the correct implementation of the move, but I'm not sure.