Interesting problem here. This is a great example of the difference between "intent' and "application" of a law.
At core issue is the fact that the "intent" of the law is to not have noise over 95dB on the street. But the way the law is written, there is a loophole because of the mode-after-on/off-cycle definition in the referenced standard. Essentially, the sport mode should not be tested for street compliance. But, the real problem is that the owners end up using sport mode on the street. That's the condundrum of the law the way it is written.
Technically, this Elantra N is compliant by the way I read the linked story. But how is a cop on the street supposed to know that??? That's not a topic typically covered in any law enforcement academy. How is a LEO supposed to know which model of car comes with a programmable mode which, by omission of law, makes the car "compliant" (only because the law is poorly written)? Is a cop supposed to have an OEM reference sheet so he can tell which OEM has selectable tuning, versus some kid in a hopped up Civic with a loud aftermarket exhaust?
Again, the only reason the car is "compliant" is because of the loophole in the law. The car isn't complaint because of the noise made; it's complaint because of a loophole. If CA wanted to close that loophole (and this example may well be the catalyst that causes it to be closed), then the owner can't use that as an excuse.
At it's core, the "intent" of the law is to have cars tested in a "street" mode; they would have to be compliant 95dB or less. And that allows the "track" (aka sport) OEM modes to be used ON THE TRACK. But the law is poorly written in that it does not specifically state ONLY street modes can be used on the street. There should be a codification written which should say "Regardless of OEM or aftermarket tuning mode, no exhaust or engine noise over 95dB is allowed on public roads." So you would "test" in street mode, and ONLY use street mode on the street. Track modes would be essentially unregulated and ONLY for the track. That way, this problem doesn't happen.
It's not the LEOs fault here. See this reference:
Assembly Bill 1824 went into effect in January 2019. This new legislation does not make California vehicle exhaust noise laws more strict. Instead, the Bill only makes it mandatory for police officers to issue immediate tickets to offenders.
California allows modifying vehicle exhaust, but up to a certain noise level. Learn all important California vehicle exhaust laws valid for year 2023.
The law makes it his "mandatory" job to issue a summons. So those of you who think the cop was overly zealous are ill-informed.
However, I don't agree with the officer's statements about spending money and sueing; that's none of his concern.
He should enforce the laws and let the civil entities figure out the rest.
If it were my car, I'd pay to have a really quiet muffler put on. That modification creates a "fix" which would trigger a re-test.
Go get the car re-tested (and presumably pass).
Take that muffler back off and go back to the stock system.
Never use anything but a street-mode on the public street; that will avoid the issue in the future.