Does anyone know the noise level law in California about motorcycle's that I can cite to an offending neighbor?

We have two bikers who roar down this residential street with their sterophonic radios blaring and very very loud motorcycles. Someone mentioned they may have a thundering (?) pipes or something?? We want to inform them of the motorcycle noise law or ordinance in Oakland California. Does anyone knw what law it is so we can cite it to these jerks?