99 Honda civic EX, manual trans. Just recently had to cut my old exhaust bolts off and replace the gasket and exhaust header gasket. But now when i drive its like at high rpm there are exhaust gases pushing through thay point and the exhaust has a slight seperation. And its loud as hell like a sratching, screaching noise. Ive replaced the hardware, a new gasket again but for some reason it still doing that. And i dont think a clogged cat converter would do that cause im still getting air through exhaust. But could a clogged cat force the air to push itself through that point. Cant seem to find anything on it or someone having the same problem. Thanks.

 

I've had the same issue with mine for a few years, the screeching mainly occurs on deceleration at high revs. I believe its the donut gasket but I've tried high temp silicone and hasn't solved the issue. It's very hard to diagnose with the car stationary