I've been having some issues since i put on a pde uppipe and turboback exhaust. I was getting a po420 code. I got the ILP fix for that and haven't seen that since. But since i did the exhaust i get a high pitched whistle coming when i accelerate hard under boost. It doesn't do it sometimes when the car is warm. But it always does it when it's cold. I know for a fact the exhaust is leaking in the downpipe on top of the catalytic converter at the flange. FIS already put in a new uppipe and gasket. That didn't fix it. Now i got a po546 code (Exhaust Gas Temperature Sensor Circuit High Bank 1 Sensor 1). I called the service department and they have me really scared saying that aftermarket exhaust on a wrx burns up the pistons, valves and egt sensors and they cost a lot. He said that cold air intakes will burn the stuff up too. I'm not made of money and i can't afford to replace engines and egt sensors all the time. I wouldn't think exhaust would hurt the car. But he also said that an exhaust leak in the downpipe would cause the air to come back through the exhaust and cool down the valves and burn them on the edge or something. Either way i'm really spooked and i've gone up to FIS from Waco 4 times now. I really need to get some anwers. The car looses lots of power when it makes the noise also. I go from 13.2-13.5 when i hear it. And my traps go from 101.6-98.7. So it looses a lot. Thanks for any input you guys can give.