I searched around a little bit, but couldn't find anything. I read about a hissing noise after installing either test pipes or HFC, but nothing on headers.

I installed Strup headers a few weeks ago (factory cats) and when i rev the engine or the engine looses revs around 2000-3000rpm or 3000-2000rpm there is a hissing noise. Almost like air is trying to escaping, but it has no where to go. Has anyone else experienced this or heard of this after header install?

 

Maybe the gaskets bad and you have a leak? Hopefully thats it..

I would go back and retighten everything, maybe try loosening it up and then retightening

 

Yeah, have you checked for leaks yet?

 

Checked for leaks...i don't see anything...

 

Since you have a 03 did you use new gaskets? Wipe/clean connections that need a gasket, then take the car for hard drive or when the car is cold started look for water leaking at those flanges.

Check for carbon build up at the areas you just cleaned if you find any then you have a exhaust leak.

 

Yeah, all new gaskets. I don't see any leaks or water anywhere...

 

The only thing left to do is look under car while someone revs to try and see where it's coming from.

One last thing to check is are your O2 sensors in tight? One may be loose.

 

lol we did that to. Put it on the lift where i used to work and the only thing we can determine is that it was coming from the cats...but we didn't see any leaks.

 

If it sounds like a rattle snack hiss than it is your Y-pipe. The flex pipes go bad and start to hiss. It happen to me and my best friend both changed out our Y-pipes and noise was gone. If you don't want to replace your y-pipe try getting some heat wrap and wrapping the flex pipes.

 

the best thing to use is sea foam to see if its leaking anywhere

did you tighten each nut to specs? ive heard that if you tighten the crush gaskets to tight, then it could cause a leak. and by loosening and retightening, the gaskets will still be crushed from the 1st tightening. might need to get new crush gaskets if thats the case.

 

Dont know what to tell you except take them off if you are sure it's from the cats.

 

You installed them yourself? maybe you can take it to the shop to double check your work.

 

I'm sorry, I stopped reading at headers + factory cats... SMH