1999 Honda Civic Owner's Manual - Page 122

Audio System Electrical interference from passing vehicles and stationary sources can cause temporary reception problems. As required by the FCC: Changes or modifications not expressly approved by the party responsible for compliance could void the user's authority to operate the equipment. Radio signals, especially on the FM band, are deflected by large objects such as buildings and hills. Your radio then receives both the direct signal from the station's transmitter, and the deflected signal. This causes the sound to distort or flutter. This is a main cause of poor radio reception in city driving. Radio reception can be affected by atmospheric conditions such as thunderstorms, high humidity, and even sunspots. You may be able to receive a distant radio station one day and not receive it the next day because of a change in conditions. Comfort and Convenience Features