It is unlawful for any person to operate a motor vehicle which shall not at all times be equipped with a muffler upon the exhaust thereof in good working order and in constant operation to prevent excessive or unusual noise. No muffler cut-out, bypass or similar muffler elimination device, exhaust or vacuum whistle shall be used on any motor vehicle while operating within the City; however exhaust whistles may be used on authorized emergency vehicles. (1988 Code § 15-304)