Now, you can argue about whether or not we should describe this with the word “sound” or “noise,” or “fersizzleplumf,” but let’s all be aware that we’re arguing about which word to use to describe reality; we’re not arguing about what reality is truly like.

No. Various people do believe that identity is part of reality. Various people believe that it's reasonble to say that in reality I existed ten years ago even if no atom in my body existed ten years ago.

Atheism is the lack of belief in theism, or sometimes, the belief that theist ideas are false. This is the nature of it.

Basically atheism has nothing to do with the properties of the average atheist that an someone doing a sociology study on atheists would find?

It's ironic that you think that atheism has a nature given what you said about reality above. That you believe sound has no such thing as a nature that can be investigated. It seems like you choose your ontological committments based on what gives you the answer you are seeking for a particular case instead of staying consistent or even going so far as recognizing that there are different possible committments.