catalytic converters

I just replaced my rear Catalyic Converter as it’s called. ( one after the Manifold one) I replaced it with an aftermarket Walker 55585 Ultra EPA Certified Catalytic Converter. I know it’s always better to keep original but unfortunately some time ago when replacing the exhaust that rusted out...

2005 outback 2.5 non turbo, federal emissions 270,000 miles with the engine rebuilt I’ve replaced both O2sensors and still have the p420 codes I am getting a LOUD buzzing sound- gonna replace muffler at the same time It looks like there is a Y junction among the converters I’m having trouble...