I just joined this forum today to offer this possible solution. I have a 2020 Leaf SV Plus and my wife and I have been beating our heads against a wall about this issue since the day we bought it.
Had tried disabling Data Transmission to no avail, but just today, I read on an Apple forum that the Zoom app was identified as a problem, and deleting the Zoom app from their phone worked!
https://discussions.apple.com/thread/251545686
So I run out to the parking lot after deleting the WHOLE Zoom app, not just the CarPlay mirror app in the CarPlay settings, the WHOLE thing.
Guys and gals....it actually worked!!! No more crackling!!! It was the ONLY thing I changed between this morning's drive to work where Siri was her good old crackly self, and now.
Curious to know if anyone WITHOUT the Zoom app is experiencing these same issues.