I have been searching and searching and never got a clear answer. What is that hissing/rattling sound I'm getting after the test pipe install? Altered Atmosphere non-resonated test pipes. Stock exhaust. Here's a vid:

 

Yeah I cant hear anything from your video.

Try taking one from outside from the side of the car near the test pipes.

but to your question, I have a similar thing with my HFCs, a hissing and a really loud rattling when decelerating, not sure what it is though.

 

it seems like it only does it at a certain rpm range as well.... hmmmm... i wonder if its coming from inside the cat cause it doesnt sound like a exhaust leak as if the gaskets didnt seal properly

 

You're hearing the nature of the VQ (ie firing order) when you open up the exhaust by either adding HFCs or TPs. It's not a sexy sound at all and LOTS of people mistake the noise for a bad flex section or broken HFC cat. Most times what they're hearing is firing order of the motor which can't be fixed You're going to have to learn to live with it or add HFCs or put the stock cats back on. You could true to add some resonators, but that could get expensive and could pose restriction. Do you also hear a faint metallic rattle under medium/hard acceleration between 2500-4500rpms?

 

Yes. i hear a lot of rasp which I expected but this noise is weird and I've only heard it on one other youtube video. This one:
I always hear mine right between 1900 and 2800 rpms.

Would getting the XO2 solve it? I can get one of those really really really cheap right now and I wonder if that will do the trick.

 

adding the xo2 and test pipes, get ready for fix a tickets. cops will here you comming.

 

lol. yea my boy has a Z with that combo and it is loud

 

If you think your car is raspy and noisy now, the XO2 will make it a lot worse.

 

it least it can be masked by overall loudness....are you the DaveB from the org?

 

Well I ended up getting the X02 and boy is it loud!!! It did make that rattling sound far less noticeable but it's still there. I loved it at first but it's just unbearable at this point and I don't race at the track anymore so it's not really serving a purpose. I made the mistake of buying some generic silencers that are on their way but I didn't know they won't fit or make a difference with this exhaust. Anyways I'm back at square 1. I'm thinking about getting some resonated test pipes and I wonder if this will get rid of the noise or at least make it bearable.

Here are a couple of clip of the current setup.

 

i have the same problem, the y-pipe seems to be the culprit. but yours arent resonated so they are more distinct than mine.

 

Interesting. That's the 3rd time I've heard that. So yours are resonated and you still have the noise? Have you ever tried changing the y-pipe?

 

I'm getting the same exact thing. I have FI HFCs and Borla exhaust. It's driving me crazy. I was actually thinking of wrapping it with heat wrap to try n muffle the noise. Has anyone tried it or think it'll work?

 

Some people say wrapping the ypipe helps but I havent heard it yet. Mine still does it and Ive tried a few different setups.