Since BONG! is often used to describe the tone of a large bell, it is thought to be an ancient term.
It actually originated in the 20th century. The middle brothers in the Crosby family, Harry and Edward, were always getting into trouble. When Harry was struck by his father as punishment, his tiny head made a distinctive BING! from his braces clashing together; therefore he gained the nickname "Bing". His older brother Bob had a larger and more hollow head that produced a BONG! noise. This accounts for their musicality since they were often hired out as percussion instruments to novelty jazz bands of the pre-World War I era.