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I would think your exhaust would have a different smell. I know my cats are gutted and the exhaust has a harsher smell then cars with cats in place.
Brian
If they sound hollow, most likely they are. If there is stuff in there, it will sound like a thud. If there is nothing it will sound tinny (not a word, but that is the best I can do right now).
The smell thing is true. My car was okay until I took the main cat off. When it is idling, it stinks.