Depends. As long as the bullet doesn't break the sound barrier, a gun can be made reasonably silent with a good suppressor, to the point where the sound of the semi-automatic mechanism operating is louder than the gunshot itself. If the bullet is supersonic, then it will still be painfully loud.

I've got a suppressed Ruger 10/22 (22LR) that's about as noisy as a stapler.

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