Although Generac doesn't provide decibel data, if you Google "Generac generator decibels" there are a number of videos on YouTube where people have done measurements and side by side comparisons. I found the GeneratorPowerSource channel to be pretty informative when I was researching a second generator that would be capable of running the AC this summer. They have a comparison video of six different manufacturers including Generac here:
https://youtu.be/MzsJ4RksYn4
If you don't care to watch 15 minutes of generator testing, there are tables of results at the end of the video.