Officer reported seeing a black, triangular object with two white lights on the rear underside and a red light on the front underside of object. officer is Cessna pilot but could not identify object as known aircraft of any type. reported it made a loud humming noise unlike any aircraft noise know to him. the lights flashed in off/on pattern as it flew overhead at about 3000 feet travelling from the northwest to the southeast at approximately 300 mph. object flew beyond observable horizon.