Metallic rattle around 1500 RPMs?

Frostydub · January 30, 2020

New to the forum. Coming from VW's so I'm used to the forum game and I've searched and searched before I posted anything. It may be out there but I haven't found it yet. Has anyone experienced an intermittent metallic rattle seemingly coming from the passenger side? Seems to happen in both V4 and V8 and also when I manually control the gears. In the video I just left it in M5 and had it shift on its own. 120k on the clock, L86, 6L80. Skip to around 1:20 to hear it best. Thanks in advance for your thoughts.

tlaw91 · February 2, 2020

Sounds like a weak passive exhaust valve spring, it’s a valve in the exhaust located just after the muffler that works with AFM for noise.

Basically just a valve on a spring. You can’t fix it you have to replace the back half of the exhaust.

Hope this helps

-Friendly neighborhood GM tech

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Frostydub · February 3, 2020

On 2/2/2020 at 9:27 AM, tlaw91 said:

Sounds like a weak passive exhaust valve spring, it’s a valve in the exhaust located just after the muffler that works with AFM for noise.

Basically just a valve on a spring. You can’t fix it you have to replace the back half of the exhaust.

Hope this helps

-Friendly neighborhood GM tech

Sent from my iPhone using Tapatalk

Ok, great - thanks! I've definitely heard the "chirp" when it switches back into V8 mode but wasn't sure if it was the rattle culprit as well. I did read somewhere where the rounded clamp that connects the catback portion to the y-pipe (I believe...first V8 so some things are still new to me) comes loose. I tried to move it around and it appears pretty solid. I did see where that valve is while I was down there. Is there a sure fire way of testing it to see if that's truly where it's coming from? Thanks again!

tlaw91 · February 3, 2020

The way I’ve found of testing that valve is to replace it and retest.

Not the answer you were looking for I’m sure however that’s how these new cars are sometimes, I’m sorry!

Me and another tech messed around with a suburban once for two hours trying to hold the spring back to see if we could lock it in place to verify that was the noise but were unsuccessful. Replacement fixed the issue.

Hope this helps!

Frostydub · February 4, 2020

8 hours ago, tlaw91 said:

The way I’ve found of testing that valve is to replace it and retest.

Not the answer you were looking for I’m sure however that’s how these new cars are sometimes, I’m sorry!

Me and another tech messed around with a suburban once for two hours trying to hold the spring back to see if we could lock it in place to verify that was the noise but were unsuccessful. Replacement fixed the issue.

Hope this helps!

Well in that case sounds like a Corsa exhaust will be on order soon! Thanks for your help!!

tarheel34 · February 5, 2020

My 2015 Tahoe started making an almost identical noise about 3 weeks ago. 120,000 miles on it. Seems to just make the noise when the vehicle is cold though. After it warms up, it’s usually always silent.

were you able to confirm that the exhaust valve was the issue?

tlaw91 · February 5, 2020

My 2015 Tahoe started making an almost identical noise about 3 weeks ago. 120,000 miles on it. Seems to just make the noise when the vehicle is cold though. After it warms up, it’s usually always silent.

were you able to confirm that the exhaust valve was the issue?

Go under your truck and the valve is right after the muffler. Turn it back and forth with your hand. You’ll hear it squeak and squawk and make all sorts of racket. That pretty much confirms it.

Try it and report back

-GM tech

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tarheel34 · February 5, 2020

Awesome, thank you! I’ll check it tonight.

Frostydub · February 5, 2020

1 hour ago, tarheel34 said:

My 2015 Tahoe started making an almost identical noise about 3 weeks ago. 120,000 miles on it. Seems to just make the noise when the vehicle is cold though. After it warms up, it’s usually always silent.

were you able to confirm that the exhaust valve was the issue?

Not yet, unfortunately. 4 kids, just moved to a new house, and I had to do a brake job on the wifes van has kept me from tinkering with this thing as much as I want to! I definitely know that it chirps when switching from V4 to V8 and that's pretty common it seems like. Just haven't gotten down there to wiggle it around to see if it's also the rattle I've been hearing. Let me know what happens to yours.

Prospect62 · February 6, 2020

Sounds like a Jake Brake! haha cool if you ask me!

No really, I'd be interested to hear if you confirm it's this valve. Looking at disabling my AFM and if I do, probably won't need the valve any longer.

tlaw91 do you see a lot of these failing?

tlaw91 · February 6, 2020

No but I’m in the south with lots of hills and traffic. Most people around north Georgia don’t spend much time in V4 mode

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tarheel34 · February 6, 2020

I clamped mine open, drove it and it’s still making the noise. When I turn it by hand, it’s not the quietest thing ever, but not too bad. Funny thing about mine is that after the vehicle gets up to operating temps it’s completely silent. Never makes a peep. It’s about to drive me crazy.

tlaw91 · February 7, 2020

I have NOT had any success affixing the valve in the exhaust make making the noise go away, unclear why I’ve never had one apart.

With that being said if you have clamped it and not changed the noise that does not necessarily mean you can rule out the valve.

It may also be exhaust alignment and or exhaust gaskets.

You wouldn’t happen to have broken exhaust manifold bolts would you?

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tarheel34 · February 7, 2020

18 minutes ago, tlaw91 said:

I have NOT had any success affixing the valve in the exhaust make making the noise go away, unclear why I’ve never had one apart.

With that being said if you have clamped it and not changed the noise that does not necessarily mean you can rule out the valve.

It may also be exhaust alignment and or exhaust gaskets.

You wouldn’t happen to have broken exhaust manifold bolts would you?

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I wouldn’t think the manifold bolts would be broken. The noise sounds like it’s coming from under the rear seats almost. That’s why I was hoping that the exhaust valve would be the issue.

the thing that keeps me scratching my head is that as soon as the vehicle is warm it stops making the noise. Until then though, it’ll make the noise 5-10 times.

tlaw91 · February 7, 2020

I’m still suspecting your exhaust valve.

There is no GM procedure for verification. If it makes the noise you are describing in the area you are describing it in, it’s the valve.

Anyways I hope this helps

-GM Tech

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