Vehicle Noise: Santa Rosa vs Sonoma

Are loud exhausts illegal in unincorporated Sonoma County?

Yes, under California state law. Vehicle Code 27150 requires an adequate, properly maintained muffler at all times, and 27151 bans modified exhaust systems that amplify noise. The Sheriff and CHP enforce these rules; the County has no separate exhaust-noise ordinance.

What about loud revving or car stereos at night?

Loud, unreasonable vehicle noise that disturbs people — such as repeated revving or a booming stereo late at night — can be cited by the Sheriff under California Penal Code 415, in addition to any equipment violation under the Vehicle Code.

Can the City of Sonoma write its own decibel rule for motorcycle exhaust?

Local jurisdictions cannot impose stricter equipment standards on registered motor vehicles operating on public roads — that field is occupied by the California Vehicle Code (CVC §§ 27150, 27151, 27200 et seq.). Sonoma PD enforces the state standards rather than a city-specific dBA cap.

Does the city regulate parked or idling commercial vehicle noise?

Yes, indirectly. Once a vehicle is off the roadway and on private commercial property — for example, a refrigerated trailer idling overnight at a market — the SMC § 9.56.040 commercial limits (65 dBA intermittent / 55 dBA constant) apply at the property line, and SMC § 9.56.030 allows enforcement of loud/unusual noises regardless of source.