CA's war on excessive vehicle noise - 2019 new law. California Vehicle Code § 27150

Yep. And it's only beginning. Another law that is subjective and not objective. How do you fight a cite based on an officer's personal impression of a sound? (Admittedly it would probably difficult if not impossible to write a technically adequate "law" that defined the (objectionable) measurable sound characteristics.)

I was a police officer in Nevada. We had (this was the 1980s, but I think it's still in effect) an ordinance titled "Loud noises from mufflers," that stated that the legislative intent was to require vehicles to operate as quietly as possible. If the vehicle had been modified from stock to make more noise than it did from the factory, it was ticket bait. I wrote several of those to drivers who had installed glass packs and similar modifications on their cars, and never lost one in court. As soon as the driver mentioned they had modified the exhaust system and that it was louder than before, they were toast.

I expect other jurisdictions have similar laws. Keep this in mind when planning vehicle mods.

Jalopnik wrote a bit on it...

https://jalopnik.com/why-people-are-suddenly-freaking-out-over-californias-e-1831620651