You don't have to reply to it, and no sense in doing it either.
If your car is of a model year that came with a cat as OEM, they'll look for it, and if it isn't there, they'll automatically fail you, even if you pass the emissions test.
Happened on an 89 Fox I had, the cat looks like a resonator.
You can get a generic 2.5" Magnaflow cat for $100, get some flanges from Dave at PP and make a test pipe the same size. Just swap in the cat for inspections, and bolt the test pipe back in for regular driving.
or i could even attach a cat casing to the car with a hose clamp, if htey ask, i'll say it was rattling.
