American who left the country over a decade ago.

Many (of course not all) speak more loudly than they think and more than is necessary. This is especially noticeable when not competing against other people’s voices/loudness in quiet places. That is, the default is higher and you might work to lower it or at least be aware of it depending upon the ambient volume and norms where you are (Americans aren’t the only ones like this).

Many US folks also act differently to even other English-speaking countries. This can be extroversion, small talk in countries that don’t do that, certain expectations of how things should work, etc. USAmericans are the folks I hear most saying “but it’s not that way in my country!” (though again, not exclusively). How direct you are vs others is another one; many can be quite direct whereas other countries use more context and subtlety. My advice would just be to watch how other people interact more intently than just being around in the space until you get used to it. I’ve never lived in Australia so I couldn’t specifically say