2012 Sierra - Hammering Sound

[schenk11]

I own a 2012 GMC Sierra 1500, 4WD, 5.3L, towing package

When letting off the accelerator for a few seconds, you can hear a sound (faint) similar to a pebble being dropped in a coffee can. Then when hitting the gas again it makes a hammering sound for 5 seconds or so and then stops.

There is no loss in power, acceleration or performance.

Two dealerships, 3 private shops can not determine the issue. Took pan off transmission, no metal or clutch plate debris can be found and the fluid is clean.

Suggestions.

 

[stevj]

Cylinder reactivation maybe?

Steve

 

[schenk11]

Just figure out watching the message center that it is the Active Fuel Management System. When it kicks down to 4-cylinders is when the knocking starts and stops exactly when it goes back to all 8 cylinders.

Adding this into the system completely stops the knocking.
Range Technology Active Fuel Management Disable Device (Blue)