I have looked over GM service information and I did find a couple of service bulletins that relate to exhaust noises.
The first of the two bulletins talks about a heat shield that is strapped onto the muffler. According to the buletin the straps could be slightly loose allowing the shield to rattle and cause a noise. The bulletin tells us to install some shims to temporarily tighten the strap and then drive the vehicle...if the noise is gone then replacing the straps will cure the noise. If the noise is still present then the shield is not the source of the noise. The second bulletin talks about a exhaust pipe joint that would be located under the passenger section of the vehicle. It looks like that joint may be mis-aligned and could cause an exhaust leak. If a leak is present then the clamp around the joint needs replacing, this should cure the leak and noise. I will post both bulletins for your reference at the end of this post.
Also you might try making sure the selector switch is in 2wd and not in 4wd. Or even see if the noise changes by changing from 2wd to 4wd or vice versa. On the chevy models this switch is on the left side of the steering wheel near the light switch. This switch is easily bumped when entering and exiting the vehicle. One of the next things I would do as technician working on this vehicle after isolating the noise to the engine would be to remove the serpentine accessory drive belt to make sure the noise was not a bolt on accessory (power steering pump, water pump, alternator, etc..).This task/job requires a trained technician to do this due to the possibility of needing spceial tools and making certian proper belt routing when reinstalling the belt. The engine can not be run too long with out the belt due to the water pump no longer being driven. Most of the things as far as repair goes will point you back at the dealer for the repair.
First ask for the technician who will be repairing your vehicle to go for a test drive with you. You may even want him to drive so that he feels and hears the vibration from the drivers perspective. This way he knows specifically which noise/vibration that you have concerns with.
Now the two bulletins are as follows.
Now the two bulletins are as follows.
| Subject: | V8 Engines -- Muffler Buzz During Vehicle Operation or Exhaust Popping/Snapping Noise (Normal Condition) When Vehicle is Hot, at Idle, or Immediately After Vehicle is Shut Off (Replace Straps on Muffler Heat Shield for Buzz Noise Only) |
| Models: | 2007-2009 Cadillac Escalade Hybrid, Escalade ESV, Escalade EXT |
| 2007-2009 Chevrolet Avalanche, Silverado (New Body Style), Suburban, Tahoe Hybrid |
| 2007-2009 GMC Sierra (New Body Style), Sierra Denali, Yukon, Yukon XL, Yukon Denali, Yukon Denali XL |
| Equipped with the following V8 Engines: |
| - 4.8L (RPO LY2) |
| - 5.3L (RPOs LC9, LH6, LMG, LY5) |
| - 6.0L (RPOs LFA, L76) |
| - 6.2L (RPOs L9H, L92) |
| Please Refer to GMVIS |
This bulletin is being revised to apply only to vehicles equipped with V8 engines and remove GEN3 engines. Please discard Corporate Bulletin Number 07-06-05-001E (Section 06 -- Engine/Propulsion System).
Condition
Some customers may comment on a popping/snapping noise from underneath the vehicle at idle or immediately after the vehicle is shut off. Some popping/snapping noise from the exhaust system during cool down is a normal condition. The noise may be intermittent depending on the outside temperature and or temperature of the exhaust system at the time of testing.
Some customers may also comment on a buzz noise coming from the muffler during vehicle operation.
CauseExhaust Popping/Snapping:
As the exhaust system cools, the muffler shell and muffler internals contract at different rates. Some popping/snapping noise from the exhaust system during cool down is a normal condition.
Muffler Buzz:
If the muffler heat shield straps are loose, the heat shield may be free to buzz.
CorrectionDO NOT REPLACE THE EXHAUST SYSTEM COMPONENTS.
Exhaust Popping/Snapping Noise:
This condition is normal to the muffler design and does not indicate poor quality or part failure.
Muffler Buzz:
Confirm the origin of the buzz by shimming (use metal shims) the straps tight and rerunning the vehicle. If the buzz concern is gone, then it is caused by the loose shield. Using the following procedure, install new straps to secure the heat shield to the muffler.
- Install three straps, P/N 10391259, so that the strap screw head will be located on top of the muffler.
- Cut off the excess strap material and bend the strap over the strap screw head.
Tighten
Tighten the strap screw to 4 N·m (35 lb in).
Part Number | Description | Qty |
|---|---|---|
10391259 | Strap, Exhaust Muffler Heat Shield | 3 |
For vehicles repaired for a muffler buzz, use the following labor operation:
Labor Operation | Description | Labor Time |
|---|---|---|
L9712* | Strap, Muffler Heat Shield - Replace | 0.3 hr |
*This is a unique labor operation number for bulletin use only. It will not be published in the Labor Time Guide. | ||
And the second....
| Subject: | Exhaust Leak/Noise At Band Clamp |
| Models: | 2009 Chevrolet Avalanche, Silverado, Suburban, Tahoe |
| 2009 GMC Sierra, Yukon, Yukon XL |
| 1500 Models With 4.3L, 4.8L, 5.3L, or 6.0L Engine |
This PI was superseded to update the repair information. Please discard PIT4859.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:Some owners may comment of an exhaust leak or noise. This concern could be caused by an unseated pipe to pipe mid joint connection, as shown below.
Recommendation/Instructions:
To correct this concern, replace the band clamp and push the pipes together while tightening the clamp bolt. The pipe flares must be seated while tightening the clamp. After clamp is installed it does not need to be perpendicular to the pipe. It is acceptable to have a pipe to pipe or clamp angle. Confirm that the clamp edges (both sides and all the way around the clamp) are seated on the pipe, as show below.
The exhaust system has a natural resonance frequency, what engineers normally try to achieve is having that resonance frequency peak outside normal operating ranges. This way we rarely hear it. One way they accomplish this is to rubber mount the exhaust system. Rubber mounting helps reduce the resonance back into the cabin of the vehicle. So we need to make sure all of the rubber mounts are in tact, and properly adjusted. By properly adjusted I mean that all mounts are free moving and not touching (grounding out) to the body or frame they are mounted from. If the one of the mounts is grounded out it allows a path for the resonance to transfer to the cabin of the vehicle. Secondly we need to check and see if your exhaust has a flex joint in the pipe. A flex joint is a short section (6 to 12 inches) of a stainless steel mesh pipe. What this type of pipe does is allow for a flexible portion of the pipe between the engine and the rest of the exhaust. GM had a service bulletin for a similar concern on some of the trucks.
If your exhaust does not have a flex joint, I would recommend having one installed. This is something a local exhaust shop would be able to do for you. And lastly we can add mass (wieght) to your exhaust to try and help change the natural resonance frequency. This is also outlined in the bulletin I will provide for you. Keep oin mind that these are not what would be considered a gauranteed fix, however your going to have to try something to eliminate the posibilities. These are a few things that came to mind today. Having the dealer that is willing to work on it for you call GM Technical Assistance is highly recommended. As you can imagine they get a much larger database of concerns and fixes.
This bulletin does not specifically apply to your vehicle, but it is a similar concern.
| Subject: | Exhaust Moan/Vibration Noise (Install Exhaust System Flex Pipe Kit And Exhaust Dampeners, If Necessary) |
| Models: | 1999-2007 Chevrolet Silverado 1500 Series Extended Cab or Regular Cab/Long or Short Box Pickups (Classic) |
| 2007-2008 Chevrolet Silverado 1500 Series Extended Cab or Regular Cab/Long or Short/Standard Box Pickups (New Body Style) |
| 1999-2007 GMC Sierra 1500 Series Extended Cab or Regular Cab/Long or Short Box Pickups (Classic) |
| 2007-2008 GMC Sierra 1500 Series Extended Cab or Regular Cab/Long or Short/Standard Box Pickups (New Body Style) |
| with 4.3L Engine (VINs W, X -- RPOs L35, LU3) and Automatic Transmission (RPO M30) |
This bulletin is being revised to add the 2007 and 2008 (New Body Style) model years, update the warranty information and add information for installing exhaust dampeners. Please discard Corporate Bulletin Number 02-06-05-003F (Section 06 -- Engine/Propulsion System).
Condition
Some customers may comment on a moan or vibration noise at low vehicle speeds 40-64 km (25-40 mph) or between(NNN) NNN-NNNNRPM under load.
CauseExhaust system resonance may be transmitted through the powertrain mounts into the body causing this condition.
CorrectionCaution: Personal injury or burns may occur when working on a hot exhaust system, let the exhaust system cool off prior to performing the repair.
An exhaust system flex pipe kit is available to correct this condition. If diagnosis leads to this condition, install the applicable exhaust system flex pipe kit listed below using the following procedure. Refer to the Parts Information for kit applications and usage.
Important: This fix and the kit part numbers are specific to vehicle frame type. A Level 3 frame was introduced interim 2000 model year (approximately January 2000). With a Level 3 frame, the transmission crossmember was moved forward of its previous location. Pre-Level 3 frames will require the installation of additional components to correct the condition.
1999-2000 4WD Models Built Prior to 1/20/00 and All 2000-2008 2WD and 4WD Models Built After 1/00
These models require the installation of a flex coupling. The flex coupling has adapter sleeves for the installation of U-bolt clamps. This procedure uses the U-bolt clamps, but the preferred installation method is to weld the flex coupler to the exhaust pipe.
- Raise the vehicle.
- Locate the first available straight section of pipe rearward of the mid-joint flange and forward of the muffler assembly.
- Measure approximately 228 mm (9 in) on the straight pipe and mark.
- Using a suitable cutting tool, cut out the marked section of the pipe and remove.
- Remove any burrs, if necessary, before installing the flex coupler pipe.
- Install the flex coupling (1). Expand the sleeves of the flex coupler, if necessary, to properly fit over each pipe end. The centerline of the installed flex coupling should run parallel to the straight section of pipe (no bends in the coupling) for optimum performance.
- Install the U-bolt clamps (2) on each sleeve end of the flex coupling.
- Lower the vehicle.
- Verify that the condition has been fixed.
Tighten
Tighten the U-bolt clamps to 30 N·m (22 lb ft).
If the exhaust vibration or moan is still present, order two exhaust dampeners, P/N 10199232, and proceed to Installation of Exhaust Dampeners, If Necessary in this bulletin.
Installation of Exhaust Dampeners, If Necessary
- Locate the bend in the exhaust pipe over the rear axle.
- Measure 102 mm (4 in) back on the straight portion of the exhaust pipe and mark the location.
- Install the two dampeners, P/N 10199232, starting at the mark on the exhaust pipe with the weights pointing up towards the underside of the pickup box.
Tip
The two dampeners should be installed close to each other on the exhaust pipe, but the dampeners should not touch together.
1999-2000 2WD Models Built Prior to 1/00
These models will require the installation of a flex coupler, two Y-pipe support brace rods w/integral U-bolt clamp assemblies on the LH and RH sides of the transmission rear mount and new transmission mount studs and nuts. The Y-pipe support braces are used in combination with the flex coupler to reduce exhaust moan.
- Install the flex coupler using steps 1-7 in the first procedure.
- Support the transmission with a suitable adjustable jack stand.
- Remove the two bolts and nuts from the transmission rear mount.
- Position the transmission rear mount and install two new studs to the mount.
- Install the new studs supplied with the kit to the transmission mount.
- Loosely position the Y-pipe support braces w/integral U-bolt clamps (LH and RH) to the underside of the transmission rear mount and the crossover pipe as shown. The top ends of the braces attach to the underside of the transmission rear mount. The bottom ends of the braces attach to the crossover pipe using the integral U-bolt clamps. The braces support the LH leg of the Y-pipe where it crosses over the vehicle to meet the Y-pipe collector.
- Install the two nuts to the transmission rear mount and the two nuts to the U-bolt clamps.
- Lower the vehicle.
- Verify that the condition has been fixed.
Tighten
| • | Tighten the new transmission mount nuts to 25 N·m (18 lb ft). |
| • | Tighten the two U-bolt clamps to 30 N·m (22 lb ft). |
If the exhaust vibration or moan is still present, order two exhaust dampeners, P/N 10199232, and proceed to Installation of Exhaust Dampeners, If Necessary in this bulletin.
Part Number | Description | Usage | ||||
|---|---|---|---|---|---|---|
15076982 | Exhaust System Parts Package | 1999-2000 2WD Models Built Prior to 1/00 | ||||
15076990 | Exhaust System Parts Package |
| ||||
10199232 | Exhaust Muffler Vibration Dampener Assembly | 2-If Necessary |
| • | Kit P/N 15076982 includes a flex coupler, two support brace rods w/integral U-bolt pipe clamps, two U-bolt pipe clamps (for use with flex coupler) and two new transmission mount studs w/fasteners. |
| • | Kit P/N 15076990 includes a flex coupler and two U-bolt pipe clamps. |
This details will help.
Thanks.
See below the latest solved car problems :----------
