It's a crack in the y-pipe, about 2" after they come together. I had the wife do some quick revs while I was under it and I could hear and feel the exhaust leak. When the engine torqued, the crack actually spread apart. I'd say there is a good chance that the cat is at least partially plugged, however, because it would seem that alot of backpressure exists to create the exhaust to flow out of that crack fast enough to whistle like that. I'm going to sleeve that cracked area next weekend and also gut the cat. What's the easiest way to gut a cat? Years ago, I had an 85 Toyota truck and I just drove some rebar "through" it and it broke apart and fell out of the housing. I remember it was a bear hitting it hard enough to bust it all up. What's the easiest way that you guys have found?

Will my O2 sensor throw a code if I gut the cat? I will see if it does - if so, I will try the antifouling inserts for spark plugs - supposedly, if you space the O2 sensor "out" a little bit, it will fool the O2 sensor into not sensing a fault.