I installed 4 1 ebay header and now I have this surging type noise. It drives me nuts. I sorted out all the leaks, checked it with the shop vac/blower side.
Tiny leak from o2 sensor and gasket. Don't think it'll cause it to make the surge /screeching sound on the acceleration.
I kept the stock cat with flanges welded.
Anyone else had this problem?

 

I have basically the same header on my car, what is the noise like? I had some leaks that I sorted out but never had a noise, when do you hear the noise?