rattling coming from the exhaust?

Hello,

Excessive restriction on the catalytic converter can make the vehicle struggle to accelerate. As the air is unable to flow properly thru the exhaust system. This can also happen due to any restriction in the exhaust system.
You can have broken catalytic material inside the converter. Which can restrict the air as well as make sound as you accelerate.

You might find these articles helpful:

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms
https://www.2carpros.com/articles/catalytic-converter-replacement
https://www.2carpros.com/articles/how-exhaust-systems-work

I attached diagrams for your reference.

Please let me know of any questions.
Thank you.