When other countries say Americans are loud, what does this mean?

I read people say online that Americans are loud. What does this mean, exactly? Is it literal volume or is it our personality/presentation? Something else?

I may be moving to Australia because of my wife’s job, and I want to better understand this. I want to assimilate and I don’t want to be annoying. I’m personally pretty low key and listen more than speak, but this is my perception of myself.