Hello, my name isXXXXX you for allowing me to assist you! Yes it is possible that the catalytic converter's substrate has broken up and rattling causing that noise. However, you may just need to replace the catalytic converter. Most of the time the cat breaks up into a few large pieces that are too large to enter the muffler. Once the cat is removed, it can be inspected to see if this is the case. From my experience, replacing the cat is all that will be required.
I hope this information helps, and let me know if you need further assistance with this.
how can i check the convertor
You are welcome Lee! You can get a rubber mallet and hit the converter. If it makes that noise, then it has come apart internally.
Thank you for using just answer again. All of us here really appreciate your continued business!