Exhaust system noise - help please.

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Re: Exhaust system noise - help please.

Postby FrederickU633 » Tue Aug 14, 2018 8:15 am

I recently had the Max Power exhaust with ceramic header, Helmholtz mid pipe, and Super Q exhaust installed on my 2013 NC Club. I am experiencing the same high frequency metallic buzz under moderate acceleration from 2000-3000 rpm. It is a very annoying sound and greatly detracts from the exhaust note under other rpm/loads. Am I to infer from the posts that I need to remove the Helmholtz and install a traditional mid-pipe?
Please advise.
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Re: Exhaust system noise - help please.

Postby Brian » Tue Aug 14, 2018 8:25 am

No, buzz is usually the description of heatshield issue. Run it on lift to track the source. In the end I think Ian's car has unusual engine noise which he is absorbing with more fiberglass, I will video his Helmholtz on return on my healthy 2007 and my bet is it makes zero extraneous sounds.
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Re: Exhaust system noise - help please.

Postby ArmS312 » Fri Dec 07, 2018 12:02 pm

I had the same issue. While doing my transmission swap I looked at the parking brake lines and one of them was in contact with the heat shield under the gas tank (right before the diff). I adjusted the parking brake lines and the sound disappeared!
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Re: Exhaust system noise - help please.

Postby BrianW297 » Mon May 20, 2019 5:07 pm

I just installed the entire system this past weekend and I am experiencing the same sound. Very tinny and metallic sounding under acceleration. "Ricey" as Ian stated. My ear seems to tell me that it's coming from back by the muffler. I carefully checked clearances all the way around the system and there seemed to be more than enough room to prevent any vibration induced noise. My initial response to what I'm hearing is that it's a heat shield, but since nothing is touching it would have to be some kind of sympathetic vibration in response to the sound.

It does seem to have gotten a little better over the first 150 miles or so, but it's still unacceptably loud. It seems to be worse when everything is cold, the longer I drive the better it seems to get. I will drive it on my commute for the week and see if it mellows out, but it is definitely not pleasant. If I was 16 it might be cool, but not at 50. I won't have time to put it back on jack stands and search for a source until next weekend. If I had known this was a characteristic of the helmholtz I probably would have opted to save some money and go with the standard mid pipe.
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Re: Exhaust system noise - help please.

Postby Brian » Mon May 20, 2019 5:11 pm

Ian's midpipe came back and proved normal when installed on healthy car, conclusion was that he has unusual engine noise (bent valve, failed EGR, etc). We switched him to normal midpipe with fiberglass resonator that is best for absorbing that, but it was a problem with his engine we were working around, not an issue with the midpipe.

Your sound description of back by the rear sounds like heatshield under the trunk, which is a common source on NC. With age the rivets that hold that shield to bottom of trunk get loose and louder exhaust will make it vibrate in sympathy. Solutions include grab it using gloves and tweak it/bend it to again put tension in the way it sits against the rivets. Another choice is remove it and use reflective dynamat or similar on bottom of trunk, removing it is pretty easy by drilling out the rivets.

BUT, it is true as explained in the product description that helmholtz is not working when cold, part of the math is temp and we use normal operating temp for the math. So, if the issue is going away once warm you might be hearing lack of the helmholtz when cold, but then again that same lack of helmholtz when cold could be making that rear heatshield vibrate in sympathy with the 120-130 range the helmholtz chamber trims down as it warms up.
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Re: Exhaust system noise - help please.

Postby BrianW297 » Wed May 22, 2019 3:28 am

I will be playing with it over the long weekend and will report back.
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Re: Exhaust system noise - help please.

Postby BrianW297 » Fri May 31, 2019 3:19 pm

Reporting back on my last email.
Last weekend I pulled the muffler and inspected the heat shield under the trunk. It appeared to be secure, but since it's only on with a handful of pop-rivets I decided to remove it to see what happened. I feel like the noise improved a bit, but I still have a bright, metallic buzz under acceleration. Here is what I've noticed:
- It seems to be originating at the passenger side rear. Strangely it seems worse at the right tailpipe as opposed to the left, although this may be my imagination;
- Placing my hand on and off the heat shield around the Helmholtz while revving to induce the buzz does not change or eliminate the buzz;
- It tends to kick in under moderate to heavy acceleration around at 2500 and starts to fade out around 3500 rpm.
- It is not apparent under light acceleration, e.g. if I'm in a line of traffic leaving a light;
- It seems to get better after I've been driving for 30 minutes or so, but it doesn't go away entirely.

I will be doing some more experimenting tomorrow. I'll have to use some wet rags or something to try and muffle hot pieces of the exhaust system to see if I can isolate the vibration. If that doesn't work I will try reinstalling the OEM mid pipe with the new headers & muffler to see what happens and them swapping in the OEM muffler with the new headers and midpipe to see what happens.
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Re: Exhaust system noise - help please.

Postby Brian » Fri May 31, 2019 5:20 pm

Check all O2 sensor connections, and dish heat shield only 3 inches around first sensor. Put a wrench on all brace connection bolts.
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Re: Exhaust system noise - help please.

Postby BrianW297 » Sat Jun 01, 2019 12:45 pm

I've been playing around with my exhaust system components. Here's what I've found
1. GWR header & helmholtz mid pipe with stock muffler: buzz is still present under increased muffling.
2. GWR header & stock mid pipe & stock muffler: nearly back to stock sound, no buzzing noted but it's so muffled that it could be there and I'm not hearing it.
3. GWR header, stock mid pipe & GWR muffler: buzz is gone, more muffled than full GWR system and has lost a bit of it's "aggression" but the bright metallic buzz is gone. If I could have this sound but just a bit louder I would be happy.

I've just been reving it on the jack stands, I still have to drop it and take it out on the road for a test drive, but my first impression is that whatever I found disagreeable was in the mid pipe.
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