According to this article California legislature asked the "Motorcycle Anti-Tampering Act." Making it a crime to ride a motorcycle with an exhaust system not officially approved by the EPA. In essence, any exhaust system other than the one that came with the motorcycle. Governor Schwarzenegger signed the bill into law this (9-28-2010). A public statement made by this law: noise is now being considered an element of pollution in the same league as smog and green house gases. Bikers beware.
For more information on Motorcycles Click Here: http://www.brevardlawyer.com/html/motorcycle-accidents.html