Forgive the bad grammar and typos, doing this on my phone.

So I put ppe headers on my 11 is350 and it already had invidia midpipe and fsport catback along with rr-racing tune. I was doing some spirited driving and then all of a sudden the note changed completely. Does anyone know what this might be? I already checked the joints for any exhaust leaks. I have to check the headers in the morning. But aside from the headers being loose (which I would assume I would notice the sound being significantly louder. It almost sounds. Like I blew the exhaust packing out or it's stuck somewhere inside the muffler now?

 

If you have a set of secondary cats in your exhaust the internals might have broken up and started causing a blockage. Same thing happened to me and it turned out to be my secondary cats.

 

^^^^He has an aftermarket mid-pipe, so no cats at all.

Lou

 

I don't have any cats. Just resonator in my midpipe and the fsport mufflers.

 

Most good mufflers use baffles vs packing so the odds of that are slim.
No codes came up?
Changing ignition timing changes when the burn occurs and that changes the tone but what you're talking about here seems odd.
You check under the hood for vacuum leaks?
Exhaust leaks ahead of the mufflers are pretty obvious.

 

Hit vtec?

 

Did u check your gasket? my Greddy axel-back's gasket started leaking just this week and the sound changed, when I jacked the car up today and unbolted the rear part of the axel-back the gasket literally just crumble and fall off... I end up replaced all the gasket between the Invidia mid-pipe to the axel-back with Greddy Exhaust Gasket, and exhaust sound back to normal....

 

We would second the notion that it's probably an exhaust leak. Sadly, most of the aftermarket gaskets that come with new exhaust parts are very lacking in quality. We have seen some cases when they don't seal properly from the first time the car is started.

Let us know what you find after some closer inspection!

 

i think mine is still not sealing right... there is a leak somewhere but i am too lazy to find it...