The left bank catalytic converter on my 2002 Chevy Subruban (5.3L flex fuel engine) has developped a rattle. The rattle resonates at only one RPM and is otherwise fairly quiet.

Is this problem common?

Is it the forerunner of a problem yet to come? (I just read the computer and it showed no codes pending)

Can I just replace one converter? (the Suburban has 140K miles)

Someone told me to tap on the catalytic converter with a rubber mallet, but I can't see how that would help.

Any suggestions?

Many thanks.