here's the thing, when i accelarating my car like between 1st through third gear i heard some "zzzzzzzzzz" noise from front of my car. sound like somewhere is leaking air. i recently install a dc header. anyone know what's happening

 

how old is ur car? its reccommended that u replace ur header gasket (to the engine head) whenever u take off the header. also make sure the header is bolted tightly to the cat (or extention pipe in some cases). if there is a leak somewhere, u can usually tell cause there will be a black streak/stain from the exhaust