What was found
(CAN) AFTER DEPARTURE, FLIGHT RECEIVED LT PASSENGER EXIT DOOR INDICATION, ACCOMPANIED BY A WHISTLING SOUND. PRESSURIZATION TO A160 WAS NORMAL. INSTEAD OF CROSSING OVER THE ROCKIES, ELECTED TO RETURN TO DEPARTURE. FLIGHT WAS NOT OVERWEIGHT WHEN THEY LANDED, AND NO PAN PAN DECLARED. FOUND DOOR NOT FULLY CLOSED, DOOR CLOSED.