'91 Prizm lights go on by themselves

Yesterday the parking/marker lights on our Prizm started turning themselves on! When I enter the car, the light warning buzzer is sounding, as it should if I had left the lights on. But I didn't leave the lights on. If I cycle the light switch on the left hand stalk, the lights go out and the buzzer stops. However, the lights come back on an hour or so later.This has happenned 3 times in one day, so far.

Can anyone shed some light on this problem?