Mission Viejo, CA Noise Ordinances: Vehicle Noise (2026)

The County's Noise Control ordinance focuses on noise reaching residential property and largely defers on moving vehicles to state law, since Section 4-6-7(j) exempts activity preempted by State or Federal law. On public highways, the California Vehicle Code controls. Section 27150 requires every motor vehicle subject to registration to be equipped at all times with an adequate muffler in constant operation and properly maintained to prevent excessive or unusual noise, and prohibits any muffler or exhaust equipped with a cutout, bypass, or similar device. Section 27151 makes it unlawful to modify a vehicle's exhaust system in a manner that amplifies or increases noise beyond Section 27150 limits, or to operate a vehicle so modified; for vehicles under 6,000 pounds (other than motorcycles), a measured sound level of 95 dB(A) or less, tested under the applicable SAE standard, complies. The County does separately regulate one off-road category: Section 4-6-8.1 of the Codified Ordinances makes it unlawful to conduct motor vehicle racing, testing, or timing at raceways, speedways, off-road courses, or drag strips between 11:30 p.m. and 8:00 a.m. Stationary vehicle noise reaching a home (such as an idling truck or a parked car stereo) can also be measured against the Section 4-6-5 residential limits.