You need a decibel meter to measure exactly how loud it is at your closest point of your property. https://www.amazon.com/Decibel-Professional-Monitoring-Instrument-Classroom/dp/B07ZHG76D8/ref=asc_df_B07ZHG76D8/?tag=hyprod-20&linkCode=df0&hvadid=416713455770&hvpos=&hvnetw=g&hvrand=2180829705780429113&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9023792&hvtargid=pla-871036694768&psc=1&tag=&ref=&adgrpid=93604213333&hvpone=&hvptwo=&hvadid=416713455770&hvpos=&hvnetw=g&hvrand=2180829705780429113&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9023792&hvtargid=pla-871036694768 Now look into your area's noise ordinances. Show the local police exactly how loud it is and that they are breaking a local civil law. Keep calling and complaining. Go to your city hall meetings and complain about the lack of enforcement if nothing is done. You may have to become a nuisance to get rid of the nuisance.
Get a level meter like this:
If you want to go the whole 9 yards for value: - Get REW - https://www.roomeqwizard.com/ - Get a UMIK-1 - https://www.minidsp.com/products/acoustic-measurement/umik-1?lang=en&gclid=CjwKCAiAhKycBhAQEiwAgf19emde-l0Agz_XCUP-MWaiL4Og90OxtC1d-z2O3pDZmGDfzusoQPNCtBoCuWkQAvD_BwE - Get EQ APO
Follow a tutorial on YouTube like here: https://m.youtube.com/watch?v=Ev1bSSL8tRA
It's not that expensive. You can record the noise with your phone and record the decibel reading on video at the same time.
Just like the poor cops sent to enforce a repeat loud noise complaint will be issued a decibel reader or how troopers will often have window tint measuring tools, the poor cops tagged to hit the local car gathering for "light violations" could be issued a Light Meter
Car exhaust volume is surprisingly hard to measure because it decays with distance from the source. Additionally, the load and speed of your engine will vary the volume level of your exhaust greatly.
This means that when you test the sound level of your car, you need a well defined test procedure that specifies engine operation, as well as location of the meter. SAE J1169 is a spec that does exactly this. Google around a little and you'll probably find a bootleg copy for free, but here's a video of someone performing it on their S2000's exhaust as a reference of what it looks like in person.
If you want to know how loud your exhaust is, buy a really basic decibel meter on amazon for about $25 and follow the procedure outline in the SAE spec (copy what the S2000 video did). Otherwise, it's a pretty safe assumption that your car is less than 95dB from the outside based on the test procedure from your year of sale. The test procedure has been updated a few times since 1977 but I think 95dB is pretty common (working from memory on that last statement).
Keep in mind that the dB scale is logarithmic, which means that seeing dB measurement values isn't quite as intuitive as you might think without understanding what the measurement represents. Here's some info on decibels.
Some exhaust manufacturers will test their exhausts and put the information in their sale ad, like racing beat does here for the NC. Note that they're not using a standardized test procedure so the results aren't applicable between all cars ever made, but as long as they're consistent in their own test procedure, their numbers should represent a decent A-to-B comparison for their product vs the stock product. But notice how low the noise level of the stock system is from inside the car in all scenarios.
Get one of these and work on knowing your own volume.