If you don't have much experience with headers and/or aftermarket exhaust, you will likely not like them.
If the stock header and flexpipe are not leaking, replacing the flexpipe will not make any difference.
It sounds like you still have the stock catback exhaust in place.
This is why you are hearing noises from the headers which is normal.
Install an aftermarket catback exhaust and your header noises will disappear!
OK, here's what (I think) I have:
The previous owner (from Southern NJ/Pennsylvania area) had removed the cat converter and put in a straight "test pipe", which is definitely illegal where I am in NYC; I am at least enough environmentally conscious (from being a motorcycle rider and former resident of a first floor NYC apartment) not to want to pollute the air like that, even if it were legal.
Replacing with a new OEM cat converter seemed very expensive, so I had a universal Magnaflow "high flow" cat welded in.
So what I have right now are:
These aftermarket (DC Sports) exhaust headers ...
... leading to the Magnaflow high flow catalytic converter ...
... leading to the OEM muffler and exhaust pipes
From multiple smoke tests, there is no leak in my exhaust system.
From what I thought is going on, the hissing or rushing-of-air sound I'm hearing during acceleration has to do with a less-than-ideal flex pipe that was likely used as part of the DC headers -> test pipe -> OEM cat back install the previous owner had used.
Are you saying that simply replacing the flex pipe would not be enough?
Why then should I not go to an OEM exhaust manifold instead of the DC Sports headers, as I suppose that would be cheaper and simpler than a different aftermarket set of muffler/exhaust pipes?
As I understand it, a lot of people install aftermarket cat back systems primarily to make things louder, which I definitely do NOT want to do. I just Dynamatted my doors, after all.
How much and what kind of a difference from the OEM engine's powerband response are these DC Sports headers making, anyway? Like I said, I do quite like the way my car responds now, I wouldn't necessarily want to "deaden" it just to make the noise go away, but neither would I want to install an aftermarket catback system that made the car either illegal or louder.