What was found
(CAN) FLIGHT CREW REPORTED UPON SELECTION OF GEAR DOWN, INITIALLY THREE GREEN INDICATED, SHORTLY AFTER, A FLICKERING OF THE NOSE GEAR DOOR (AMBER) AND UNSAFE (RED) AND HORN SOUNDED, THEN CLEARED. ON TAXI IN SNAG RE-OCCURRED AND GREEN GEAR SAFE LIGHT NOW U/S. ALTERNATE VERIFICATION LIGHTS INDICATED GEAR SAFE. MAINTENANCE FOUND CARD FAULT ON PSEU. REPLACED AND TESTED UNIT AND COMPLETED GEAR SWINGS WITH NO FAULTS FOUND. AIRCRAFT WAS RETURNED TO SERVICE. SNAG RE-OCCURRED FOUR FLIGHTLEGS LATER WITH INDICATION OF GEAR UNSAFE ON TAXI. AIRCRAFT IS CURRENTLY IN HANGAR BEING INVESTIGATED.