WHILE BACKING OUT OF THE DRIVEWAY, IN REVERSE, THE CAR SUDDENLY AND WITHOUT WARNING ACCELERATED AT A HIGH RATE ON IT'S OWN WITHOUT DEPRESSION OF THE ACCELERATOR PEDAL. BRAKES WERE APPLIED AT FULL FORCE DURING THE ACCELERATION WITH OUT EFFECT. VEHICLE CONTINUED DOWN THE DRIVEWAY, CROSSING OVER THE STREET, THEN JUMPED THE OPPOSING CURB, STRIKING A STONE WALL.