Flapping sound when decelerating at low speeds, between 20km/h-50km/h. Sound is only present when throttle is let off, as sound as load is put back on the truck the sound stops. Sounds like it could be coming from rear end but hard to pin point while driving.

 

#PIT5404G: Squeak Chirp Whistle Rattle Type Noise from Rear of Vehicle (Passive Exhaust Valve) or Buffeting Vibration Drone Exhaust Tone Change Body Pressure Booming (AFM Exhaust) - (Nov 20, 2020) Subject: Squeak Chirp Whistle Rattle Type Noise from Rear of Vehicle (Passive Exhaust Valve) or Buffeting Vibration Drone Exhaust Tone Change Body Pressure Booming (AFM Exhaust)
Brand:

Model:

Model Year:

VIN:

Engine:

Transmission:

from

to

from

to

Cadillac

Escalade

2015-2017

All

All

6.2L

All

Chevrolet

Silverado 1500

2014-2017

SOP

12/14/2016 for Plants G and Z*

4.3L or 5.3L

All

Chevrolet

Suburban

2015-2017

SOP

7/1/2016

5.3L

All

Chevrolet

Tahoe

2015-2017

SOP

7/1/2016

5.3L

All

GMC

Sierra 1500

2014-2017

SOP

12/14/2016 for Plants G and Z*

4.3L or 5.3L

All

GMC

Sierra 1500 Denali

2014-2017

All

All

6.2L

All

GMC

Yukon Models

2015-2017

All

All

5.3L or 6.2L

All

* For Build Plant Information See 11th Position of VIN

 

Involved Region or Country

North America and North America Export Regions

Condition

Some customers may comment on any of the following concerns:

• Squeak, whistle, rattle or chirp type noise from the rear of the vehicle
• Exhaust tone change or exhaust drone type noise
• Buffeting vibration or body pressure booming

These concerns may be most noticeable when the engine transitions in and out of Active Fuel Management (AFM) mode, or while the engine is operating in V4 (4-cylinder) Active Fuel Management (AFM) mode in the 1,100-1,400 RPM range.

While some slight changes in exhaust tone and/or vibration/drone type noises can be normal when the engine is in V4 mode, there have been complaints of them being excessive.

Note: If the concerns are excessive, they may excite the roof sheet metal and compound the issue. (See the latest version of PIT5318.)

Cause

These concerns may be caused by the Passive Exhaust Valve (PEV), located in the exhaust muffler and tail pipe assembly, making noise or effecting exhaust tone, or may be caused by an exhaust leak at the clamp joint.
Correction for 4.3L and 5.3L ONLY:

1. Verify the concern is present Only during V4 mode. (During evaluation, monitor Instant Fuel Economy screen in DIC, or on scan tool to determine V4 vs V8 mode.)1.1: Once the concern is duplicated in Drive, shift trans into manual 5th or 6th to operate in V8-only mode and re-test under same conditions.
   
   1.2: Switch back and forth between Drive and manual 5th or 6th to turn concern On/Off.
   
   Note: Using a Pico scope, AFM V4 mode operation will display as E2 for a V8 engine, and E1 for a V6 engine.
   
   If the concern is qualified to be present only during V4 mode operation, an updated exhaust to address this concern is now available for vehicles built before the build dates listed. See Notes following before proceeding to Parts table in this PI.
   
   If the noise is not present during V4 mode operation, it may occur during transitions between V4 and V8 modes - as a Test Only, perform the following diagnostic steps:
   
2. Temporarily lock the PEV in the open position, as shown in the latest version of PI1201, and re-evaluate. If the noise is eliminated or changes greatly in severity, an updated exhaust and PEV to address this concern is now available for vehicles built before the build dates listed. See Notes following before proceeding to Parts table in this PI.

Note: The updated design exhaust has the passive exhaust valve (PEV) located in front of the muffler; the original design exhaust has the PEV located behind the muffler. Proceed to the Parts Information table in this PI.

Note: Ensure there are no leaks at the exhaust band (Norma) clamp joint after the new exhaust has been installed. It has been found in some cases that a leak at the clamp joint could allow some level of exhaust tone change or exhaust vibration/drone type noise and/or buffeting vibration or body pressure booming to occur. Refer to latest version ofPIP5442. If no exhaust leak is found, replace the exhaust. Proceed to the Parts Information table in this PI.
Don't know if this is the noise, but it might be worth a look. Hope this is helpful.