Originally Posted by THE BULL

Correct.

You should be able to monitor your A/Fs to find out if they are operating at all.
Going from a normal sound to a weird sound can be a leak, it can also mean that the cats are done and they messed up the A/Fs as they went.

With the cats clogged the A/Fs will take a beating many times overheating, you can monitor catalytic temp through the A/F sensors.

Any issues with these sensors will usually send the engine into default fuel parameters which mean pig rich airfuels.

I suggest you monitor the A/F readings then take off your exhaust and check those cats.