Sonoma County, CA Noise Ordinances: Vehicle Noise (2026)

Sonoma County does not regulate motor-vehicle and exhaust noise through its own ordinance for the unincorporated area; this field is occupied by the California Vehicle Code, which applies uniformly statewide. Vehicle Code section 27150 provides that 'every motor vehicle ... subject to registration shall at all times be equipped with an adequate muffler in constant operation and properly maintained to prevent any excessive or unusual noise,' and that no muffler or exhaust system 'shall be equipped with a cutout, bypass, or similar device.' Vehicle Code section 27151 makes it unlawful to modify an exhaust system in a way that amplifies or increases the noise so the vehicle no longer complies with section 27150 or exceeds the applicable noise limits, and prohibits operating a vehicle with such a modified system. Enforcement is carried out by the Sonoma County Sheriff's Office and the California Highway Patrol. The County's own General Plan Noise Element reinforces this approach: Policy NE-1j directs the County to 'encourage the California Highway Patrol to actively enforce sections of the California Vehicle Code relating to adequate vehicle mufflers and modified exhaust systems.' Beyond exhaust and muffler issues, loud, unreasonable vehicle noise such as repeated revving, stereo noise or honking late at night can also be addressed by the Sheriff under California Penal Code section 415 (disturbing the peace).