This.

Full restaurants in Italy are a deafening cacophony. It's an arms race amongst people already accustomed to yelling at eachother on a daily basis.

There are cultures in the world that are more obnoxious and more "impolite" than American in my humble opinion (and I'm not implying anything about Italian culture here). However, I think the distinction of noise in America is that it's a cheap way to make people excited, and it wears people out over time.