2004 Pontiac Grand Prix exhaust

You would have to raise car, put on stands and inspect the exhaust system.

There is no reason to think the converter is bad as long as you are not getting any warning lights (check engine).

It may be a loose/bent exhaust shield. Try using an inspection mirror, after driving use mirror and look at convertor, if it glows red, then you may have a partially clogged convertor, but that should cause other problems like hesitation and possible misfiring.

Check your owners manual, some cars will produce a clicking sound as solenoids in EVAP operate even after engine is off and is normal.