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.