http://www.ncbi.nlm.nih.gov/pmc/arti...005793/?page=1 - according to this article it is mainly CO2 - the noise is from the bubbles collapsing almost as soon as they form.
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http://www.ncbi.nlm.nih.gov/pmc/arti...005793/?page=1 - according to this article it is mainly CO2 - the noise is from the bubbles collapsing almost as soon as they form.