My 96 Sportage had a rattling noise too, thought it was the heal shield and it turned out that the guts of the catalytic converter were rattling around inside, and sometimes blocking the airflow causing me to lose a lot of horsepower!

Maybe a local muffler shop will check the cat for you for free and tell you if it's bad. The shops here do that.

2002 Sportage 4dr 4x4 soon to undergo an Extreme Makeover!