.22lr bolt or break action rifle shooting subsonic rounds or even better yet (especially at 30yds) shooting CCI .22lr Quiet rounds.
The .22lr Quiets generate around 68db of sound - even in a carport its not going to be loud enough to make your ears ring although it'll still be pretty loud under a carport.
Otherwise keep hearing protection near your rifle. A pair of muffs doesn't take long to put on and are a good investment.
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