The primary sypmtomm of a clogged cat would not be a restricted sound. If you cat's clogged, you will lose a lot of power. A real lot of power. Example. if you take your cat off and it isn't clogged, chances are you wont ba able to feel much of a difference while driving... maybe a little, but not much. If your cat's clogged, and you do a test run without it, the difference will feel like you slapped a supercharger onto there.

But don't do anything more than a testrun around your block. Running around without a cat is borrible for the environment and a big, big fine if you're caught.