I had a shop piece together an exhaust setup for me a little bit ago. I went with a Vibrant 2.5" high-flow cat, Magnaflow 14" (body length) resonator, OBX twin-loop muffler, and 2.5" piping. I also have a CAI and stock header.

When the exhaust was first put on, I thought it was a little louder than I wanted, but sounded good overall and I was very happy. However, about 1-2 weeks after the install my check engine light came on. I hooked up the OBD scanner at Advance Auto Parts and it read the code for a bad cat. Then, shortly after that, I started to notice an EXTREMELY annoying buzzing/rattling sound, which only seems to happen between 1500-2000 RPMs under acceleration.
A friend of mine was telling me not to even put the high-flow cat on there in the first place, and to just go with a 2nd resonator if anything. He told me that the cat probably blew out already and thats why I got CEL. Upon doing some online research, it seems as though a blown cat can also cause the buzzing sound...but what is the likelihood of a Vibrant cat blowing out after only a week?!

Or do you think that it is actually the muffler and not the cat?

I was ready to buy a 2nd resonator and take it to a shop and have them replace the cat with it (and add non-foulers) but before I do that I want to be certain this will cause the problem, and not leave me spending money for no reason.

 

Not sure whether or not this is important, but if I rev at idle I do not hear the buzzing...only when the car is actually in motion.

 

Well you need to isolate the noise first could be the Cat, The placement of the entire exhaust, alot of factors, if you got pictures of the underside of the car when its on the lift i would help. Remember the engine light is on due to the Hi Flow Cat (there is a Remedy for this)

 

I do not have a lift nor access to one; but, I can jack the front of the car up and take some pics if it would really help identifying the cause...

What is the remedy for high-flow cat CEL? Installing non-foulers?

 

resonator or highflow cat.

i have same issue with my highflow Megan cat

 

So I am learning the consensus is that it is very common for high-flow cats to blow out after only 1 week?...

 

No lol.

Op it sounds like its almost for sure the cat.

Also another reason for exhaust buzzing that hasn't been mentioned above is that when you smash your headers ( be it from bottoming out/ big bump ect.) and you flatten the bottom of them slightly (under the sump) and they will be slightly rubbing together- will buzz at certain revs. happened to me.----that's for a b series anyway.

 

Well you say "no" but then go on to immediately say that is IS most likely my cat causing the buzzing...doesnt make any sense to me. Sounds like you are contradicting yourself.

And my headers have not been smashed at all, in any way. I checked.

 

So I am learning the consensus is that it is very common for high-flow cats to blow out after only 1 week?...


Sorry, I should have quoted this then saying 'no'.

 

^Still dont understand what you are trying to say...

 

Might be the heat shield if their is one.

 

Ok so I took the car to a friend's shop who made some time to look at it on the lift for me. After banging around a little bit, he came to the conclusion that the flex pipe is causing the buzzing. He said it was splitting and breaking apart, and causing a harmonic vibration (which is why it only buzzes in a 500 RPM window).

So here is what I am looking at:
-replace flex pipe
-add second 14" resonator (to quiet it down a little)

Can anybody give insight as to how much this should cost (including the price of the resonator and new flex pipe + install for both)? I have received estimates from two places, but both seem to be much higher than I expected...