A few weeks ago, my roommate and I installed Kinetix High-Flow Cats and Japtrix Y and B pipes on my 04. Since then, I've noticed a loud "fluttering" noise coming from under the car when under hard acceleration. I can't tell if the noise is coming from a certain side of the car. The noise...probably the best thing to compare it to would be a baseball card in the spokes of a bicycle. Just a rapid metallic fluttering noise. It only occurs at WOT, and is most noticable in 2nd and 3rd gear. Any ideas on this? It is a definite fluttering noise, not rasp or a hissing exhaust leak.

Any input would be appreciated.

 

I just started noticing this with my quieter exhaust system. My previous one was so loud it covered the noise, I guess. I have an aftermarket Y-pipe, Test Pipes, and Tanabe Exhaust (Mid Pipe and Muffler). When installing them I noticed the Fujitsubo Y-pipe did not perfectly match the diameter of the Tanabe Hyper Exhaust. Perhaps the change in airflow causes fluttering? Perhaps the increased flow from aftermarket parts (especially, test pipes and hi flows) cause this?

 

From reading a previous thread, I'm thinking it may be the increased airflow as well. Some people were reporting a noise similar to the one that I've had after installing ONLY their test pipes or high-flow cats, and said that it was just the extra air passing through the pipes. I'm not sure I buy this theory though. I may just take my car to an exhaust shop some time soon and see what they have to say...

 

I have tried 2 different y-pipes now, both making some sort of increase. But I feel the the thickness of the tubing on the first pipe was to thin, causing the what you call a flutter. To me it was a resonating rasp inside the pipe readily heard inside the car. My current set up does not have the inside pipe rasp, but rather you can hear a little rasp in the upper rpm's out the tailpipes now.

 

I had the same noice when i installed just my test pipes, it got worse when i did headers and y-pipe and now that i put the Blitz Exhaust on its so loud i cant hear it anymore

 

lol @ Vash

So you had the same baseball-card-in-the-spokes sound though? Maybe it IS just the test pipes/cats...

 

Here's a no cost way to narrow it down, put the stock cats back on.

 

Good point, but a PITA. Did you notice the noise with your Kinetix cats vfr350?

 

I got the same noise. H/Kinetix hi-flo/Borlar TD exhaust/

 

Yes I had the same "flutter" sound with my 1st y-pipe/cat combo. I then when back to stock for a bit, only to really notice the "choke". I then added the Kinetix cats, stock y-pipe, and notice the "rasp" more but it seemed to fad once the car was warm. Now with the Gruppe S y-pipe the rasp never goes away, but it is only present above 3000 rpm, has a nice growl down low.. I have a set of Pro 1 headers to install next, we will see what happens then. I am thinking at this point my only hope is to tune the "rasp". My next step after headers may be a b-pipe with a good resonator, or try and replace the stock resonator with a glass pack, but not sure yet. One thing seems to be certain, stock cats control the "rasp".

 

I just put in an RSR exhaust, and under hard acceleration my car sounds like a flat 4 horizontal (WRX Impreza).... Is this normal? I LIKE the sound though

 

I should clarify, with my current set up, the rasp is really only present under aggressive use of the throttle. Taking it easy up over 3000 has no real rasp.

 

Try swapping out parts until you find the one causing the problem. If still not found try removing the aluminum heat shields above both cats and maybe the one above the exhaust as well. It's a painful process but you're bound to find out what's doing it eventually.

Also, I don't know if the Kinetix cats have mounts for the OEM bracket, if not consider having some welded on to help absorb vibrations there.