I tried searching for a proper rating and it seems like no one has a proper answer. Would be interesting to see if there's an actual measure of how much noise a modern sport bike makes. Even some tracks have a 108db max.
Your google function must be broken. Search for "stock dB level" on the motorcycle of your choice and your query will be answered. You'll also come across charts with dB levels of many of the aftermarket pipes, with measurements at 6 feet, 16 feet and other distances.