Thanks to all who responded to my engine rattle query of last week. Turns
out that wily List veteran Joel Walker had the correct diagnostic vision.
The catalytic converter internal structure had disintegrated into multiple
chunks of hard honeycomb. These lumps proceeded to bounce around in the
shell of the converter simulating a can of rocks being shaken. An ugly
sound. Even after replacing the converter I still heard the noise
which  puzzled me a bit. But I realized that a few of these chunks blew
into the muffler and were jangling around  until they got small enough and
eventually blew out .

Rick Koller