Catalyst rattles inside
 

My converter has a rattle. How can I eliminate the noise?

Welcome aboard!!:icon_toast:

New catalytic converter(s)!!

you can't it's the material inside the cat, the honeycomb structure has cracked and is in pieces. As the cat gets hot the rattle will cease as the parts expand.
But yes, time for a new cat.
How old is the car, may still be under emissions warranty.

Rattle inside? Two ways, gut the cats or buy new ones. If you gut them they will remain in place buy may fail smog and/or throw a check engine light.

What if I saw off the Exhaust Pipes, past the Cat Converters, then break-up the ceramic part with a steel rod and hammer. Then run the engine and blow out the ceramic parts.

How would this affect the engine performance?
Would it still run smooth?
Would it use more gas?
Would a need to buy a tuner?

Year? Engine?

Catalytic on 2006 V6
 

Many cars have an oxygen sensor at that part, so gutting the catalytic converter will cause the sensor to end up throwing a code.

You can look for another midpipe with the catalytic converter someone might be selling from their car or get a new catalytic converter as mentioned before.

You can gut them if your state doesnt require inspections but it will set a code for catalyst inefficiencies