Verified answer

On a 2003 your check engine light should come on long before you even see/hear cat symptoms. you'll get a catalyst efficiency code P0420. Sometimes you'll hear them rattle as the catalyst block becomes loose, but like I said 9 times outta 10, your friendly check eng light will let you know somethings going on.... Your 02 sensors are what monitor the cats operation.

One symptom is not have power, engine bogging down, if that is the case have someone by tail pipe and push accelerator down see how much exhaust is coming out may not be much. If converter isn't making noise, more than likely converter isn't your problem. Your check engine light will come on, when checked would give code for bad Catalytic Converter.

if the internals are damaged, you may see small pieces come out the exhaust. otherwise, when the converter gets bad, it can cause rough engine operation, and on some occasions, it will turn red from the heat building up inside if its clogged up. its doubtful that you would need one on that vehicle at this point, unless you have an incredible amount of miles on it, or been running questionable fuel in it

They normally rattle when you rev the engine, or get someone to stand at the back of the car near the exhaust pipe while you rev it and if they see little specs of silver coming out then its broke and needs a new one

hook a vacuum gauge up to engine observe reading at idle slowly rev engine to 3000rpm observe reading if the reading is less at 3000 rpms than idle you have a clogged exhast system more than likely the convertor