Section 37
SEC. 37. All motor power shall be stopped in every motor vehicle whenever the same is unattended on any highway. Whenever a motor vehicle passes through thickly populated districts of any municipality or barrio or through the streets of any city the "muffer," if the vehicle be propelled by an internal combustion motor, shall not be cut out or disconnected and no unnecessary noises of any kind shall be given off, emitted, caused, or made by any motor vehicle at the times or in the places in this section described.