It shall be unlawful for any motor vehicle to pass through the zone with a muffler or exhaust pipe open, or for the driver thereof to blow a whistle or horn, or ring a bell, while passing in or through the zone, except to prevent an apparent accident, or to make any other unnecessary or unusual noise, or for the driver of any bus to sound its horn while in or passing through the zone, except to prevent an apparent accident.
(1980 Code, § 30.802) Penalty, see § 96.99