[Xyebo]

Hey, all


I have a 2018 V6 with a non-NPP exhaust system.


I started noticing a weird rattle coming from my exhaust area under certain conditions.

• When I cold start, I hear the rattle as the RPMs go down at around 1500 RPM mark
• Randomly, for a second or two, as I lift off the gas pedal in-between 1500 and 3000 RPM

See the video illustration in the link. At 0:04, you hear the start-up rattle that goes away. At 0:13 and 0:27, you hear a random rattle at low RPMs on/off throttle.





I won't be able to jack up the car for a few days to see if anything got lose.
What could be the culprit?

[arpad_m]

You can change the thread title if you edit your initial post in the advanced editor.

The first thing I would check is heat shields and metal covers along the exhaust. Also, even though your car does not have NPP, it still has AFM valves (up the exhaust path), and I recall some people mentioning rattles from those.

[Xyebo]

Originally Posted by arpad_m

You can change the thread title if you edit your initial post in the advanced editor.

The first thing I would check is heat shields and metal covers along the exhaust. Also, even though your car does not have NPP, it still has AFM valves (up the exhaust path), and I recall some people mentioning rattles from those.

Thanks for the tip about the title.
The shield is the first suspect, so I will look at that. Also, I don't think the manual V6 has Active Fuel Management. Am I wrong?

[arpad_m]

Originally Posted by Xyebo

Thanks for the tip about the title.
The shield is the first suspect, so I will look at that. Also, I don't think the manual V6 has Active Fuel Management. Am I wrong?

Ah, I missed that you have an M6, sorry.

I'm not actually sure if the valves are still present but unconnected, or you have a clear path. Here is a shot with the AFM valves in place in front of the differential, you may want to check.

Heat shield rattle is more likely anyway, based on the noise. I had NPP valves rattling on mine (been fixed since then) and it was nowhere as bad as this, AFM valves are the same part.

[Gen6cyl]

I was right there when I changed my diff. oil. Nothing there , just pipe

[Xyebo]

UPDATE:


I got my car up the ramps and had my friend rev it up in many different ways. The noise was coming from within the resonator.


The fasteners, the heat shields, and the hooks at seem to be held in place well. Also, I knocked on all the exhaust parts, from cats to the exhaust outlets, and I hear noise when I knock on the resonator.


Since it doesn't affect the driveability and since the sound is heard only under specific few conditions in high echo areas (and only with windows down), I will just let it be.

[T Rex]

You could bring it to an exhaust shop and have them try to tack weld the little nipple area in the middle of the resonator. Common issue where they crack in that spot.

[BOSE ZO]

Originally Posted by T Rex

You could bring it to an exhaust shop and have them try to tack weld the little nipple area in the middle of the resonator. Common issue where they crack in that spot.

Looks like mine has done the same thing, took 117k to doit though. I'm going to see a shop and try welding the drain as well.

[DIYguy]

Mine had the exact same rattle, only worse.
It wasn't the heat shields (checked) or hangars (checked) or anything of that sort.
No visible cracks or splits anywhere.

The spring loaded "valves" (mine are not motor-controlled) in front of the differential were definitely rattling.
So I wired them permanently open using fence wire.
Then it was much better, but not gone.

My next move was going to be to thread the resonator drain hole and put a bolt into it to try to apply pressure to whatever is inside it.

But right about then someone else "fixed" it for me by tapping us at a stop light in traffic.
Small scrapes and scuffs on the rear bumper cover were the only significant visual damage.
However, their low-placed bumper (older car) just barely clipped and bent the left outlet pipe.
Their insurance thankfully paid 100% for a repaint of the cover, replacement of the honeycomb energy absorber structure (which did its job perfectly) and the entire exhaust system past the cats.
It is all one giant welded piece and the body shop said they could not straighten it without cracking it.

Long story short (yes I know, too late... ) the rattle is gone.
So it was something either in the resonator or muffler, not totally sure.
But my strong suspicion has been that it was the resonator.

I hope this helps you.

[Bumbleboy92]

I had both this issue and the AFM valve issue. For both, I went to an exhaust shop and had them delete the AFM valves with plain tube (v6 AFM are spring controlled and not electrically controlled like v8) then when I had the same resonator rattle I replaced it with a X-Pipe

[Sortiez]

probably hangers, thats what mine was. sounded similar. try to move around your exhaust a bit around the hangers i believe the rubber inside starts to squeak/rattle

[Ski Mask]

Originally Posted by Xyebo

UPDATE:


I got my car up the ramps and had my friend rev it up in many different ways. The noise was coming from within the resonator.


The fasteners, the heat shields, and the hooks at seem to be held in place well. Also, I knocked on all the exhaust parts, from cats to the exhaust outlets, and I hear noise when I knock on the resonator.


Since it doesn't affect the driveability and since the sound is heard only under specific few conditions in high echo areas (and only with windows down), I will just let it be.

I have the same issue with the resonator. At first, the sound wasn't that much to make it a big deal so I let it be, its similar to the sound u have, but right now the sound got worse and every time I go to 3k rpm it makes that ugly vibrating noisy sound and its sooo loud.

For some reason on a cold start sometimes it pops and sounds really good.

I would suggest that you replace it because it will only get worse like mine.

[Gen6cyl]

Replaced my resonator with x pipe last spring ,noise gone, and put on mbrp axel back. Sounds great now.

[Roddrz]

The rattle is gone after replacing, GM Part - GM Faurecia G4-4994 Resonator, with a Lawson Industries 66925 X-Pipe.

IMO, GMs' Faurecia resonator appears to break down from heat build-up, maybe from flow restriction? The first half of the resonator is dis-colored and looks like a rainbow from being over-heated

IMO, The new X-Pipe's sound is deeper, fuller and richer.

The vehicle does feel like it gained HP.
X-Pipe also reduces output resistance by 50%.

Parts used to Fix $150 US - 8 hrs Labor - Easy to do

1) Lawson Industries 66925 X-pipe

https://www.amazon.ca/dp/B003M2IKVE?...roduct_details

Used a sawzall.

Cut the tip off of the blades to approximately 4" total length, so as to stop from hitting the drive shaft and heat shields.

1.1) The X-Pipe fits over the existing 2.5" OD pipes that were going into the rattling GMs'
Faurecia resonator

1.2) The X-Pipe exits into a 2) 2.5" Adaptor, then a 3) 45 Degree Pipe and then into a 4) 2.25" Coupler

2) Qty 2 | Adaptor 2.5" | OD x 2.25" ID

3) Qty 2 | 45 Degree Pipe is an A-KARCK Exhaust 45 Degree Pipe 2.25" OD 2 Pack

https://www.amazon.ca/dp/B0CC943YTJ?...t_details&th=1

4) Qty 2 | Coupler 2.25" ID

5) Qty 2 | 3" Hose Clamps for heat shield

6) Qty 2 | Metal SawZall Blades.
Cut the tip of the blades off to approx 4" to clear hitting the drive shaft and heat shields.

Clamps or Weld

7) Qty 4 | 2.5" Exhaust Clamps

8) Qty 6 | 2.25" Exhaust Clamps



Roddrz