Hey guys,

So, in addition to my previous post a few weeks ago about a phantom exhaust noise, I did some work and got a bit of an update, but it's still making the noise. So maybe we can see what's up..

I smacked the exhaust system off a curb (long story) and ever since then, I've noticed this noise. When hit, the muffler was hanging there due to hitting it off of the hangers, but they easily hung back up..

So, I went under the car and checked all bolt tightness. Muffler section, all flanges, header to block bolts, etc. If there is a flange in the middle of the header, I didn't do that one. Forgot to look.. Is there one on the stock header/dp? I also replaced a few hangers as well to tighten everything up..

The noise is very hard to describe. It doesn't sound outrightly like an exhaust leak, as I've heard plenty of those. And the noise seems to be coming from under the dash / passenger side area.

The exhaust purrs super smoothly at idle and cruising, but makes the noise as soon as you accelerate. It's not a rattle or anything. I checked all of the heat shields and stuff.. It's kind of an airy noise, but nothing like a hole in the exhaust. Could I have a smashed gasket or something somewhere? I have 75k on the gaskets in the exhaust ,and they were tampered with several times. I've had a few header/dp combos as well as a few different cat-backs. So maybe they finally **** the bed?

Oh, and the car still has full power and throttle response, so no issues as a result of the noise. Just.. noise.

Any suggestions guys? Thanks!!

 

Check the flex-pipe. Its located where the catalytic converter bolts to the exhaust manifold. You can easily see it from under the hood. You may have bustedthe flex-pipe and have an exhaust leak from there.

Other than that I'd say a good visual of the whole exhaust while the car is on a lift. Look for black soot on the piping, flanges and on the muffler. Also check the heatshields that're fastened to the body to make sure they're not contacting anything.

 

Cool man, sounds good! I'll look into it.. Thanks!

Any more suggestions??

 

I have this too, when I accelerate between 1500-3000.

I tightened the bolt for the heatshield last night, and it made minimal difference. It's odd though, sometimes it does it and sometimes it doesn't.

I'm out of ideas.

 

Mine seems t obe a very slight gasket air leak (the gasket between the upper and lower header pieces), but also bad insulation. I had a wreck a few months back, and the shop that "fixed" it basically seemed to have left out some insulation. Awesome.

 

I had a similar noise and when I took off the DP I was able to see that a collar had come loose just above the flexpipe. I was searching for pics but didn't find any.

 

I tried to do a ghetto fix to see if the gasket and/or insulation was part of the issue. We shall see when I take it for a spin..

 

I've found that my ZZP header-dp connection needs to be re-torqued over time as it loosens up. I was having the same problem with the stock 2-bolt catback connection, and welded it because it kept leaking no matter what i did to it.

 

Could be an internal rattle.

 

Trust me, it's not a rattle. It's an actual noise directly related to the air flow in the exhaust. It's at the same rate as the gas pedal depression, so I'm figuring a smashed gasket or some type of flange issue..

 

my room mate also has a cobalt and had that same noise as you described (passenger side under the dash). his eventually led to his flex pipe having a leak. wasnt bad at first but progressively got worse until it sounded like he had no cat and no muffler. i bet you have a minor leak in your flex pipe.

 

That's kinda what I assumed. But everything looks solid around there..

How'd he eventually fix it? Whole new header piece?

 

hit a flat spot in the nut with a center punch. That will keep it from backing off.

 

i'd bet it's ur flex pipe.

 

If the flex pipe is "damaged" can the flex piece it's self be replaced or do I need a whole new header and/or downpipe? Can't remember exactly how it's set up..

 

there is a small recall on the cat. It breaks on the inside and gets clogged, sounds like a rattle, or metal grinding sound while driving? go to the dealership and tell them about it. Getting mine fixed monday