As European travelling in Asia at the moment, I notice this a lot.

• Americans tend to speak louder, especially in groups
• You seem to speak with deeper voices. But that could also be just my imagination.
• You seem to speak more since you do a lot of small-talk. That's something not so common in other countries.
• And since many people speak English, maybe we just notice it more since we can understand it. When there are let's say loud Chinese around, it's more like a background noise.

There are loud people from all countries, and Americans are at least pretty nice usually. But in my opinion it's true, you are also louder than most.