I BELEIVE ITS SPUN BEARING OR BEARINGS..BUT WOULD LIKE TO KNOW FOR SURE BEFORE INVESTING THE MONEY INTO IT.....SOUNDS LIKE METAL POPCORN JUMPING IN THE MICROWAVE MY BRO RAN IN IT WITH THE OIL EXTREMELY LOW AND TRIED PASSING A CAR AND BOUT 3000 RPM AND NOISE FROM UNDER THE UNDER AND CAR SHUT OFF...