In June of 2018 the California Assembly voted to approve the bill AB 1824. Among other things in this bill, it changed the way that police officers are to handle pulling over someone with a modified exhaust system.
Before January 1st, 2019 (when the bill went into affect), if you were pulled over with an aftermarket muffler that was thought to be over 95 decibels the officer could give you a fixit ticket. This allowed you to take care of the excessive noise and get it signed off or to talk to another officer if you thought the first was unfair.
Now if you get a ticket it is an automatic $1,000 fine. You also need to take the car to a state referee to prove that it has been put back to stock before you can register the vehicle with the DMV. You can take it to court, but that is a lot of extra hassle to try to fight something that had been seen as a minor violation.