I think this is what you are hearing guys.
Active Tuned Mass Modules, ATMMs, which are essentially little cans bolted to the frame rails on either side of the truck, with solenoid-activated weights inside.
As the HEMI engine’s Multi-Displacement System kicks in, and sends the truck into four-cylinder mode, an underhood sensor picks up unwanted vibrations, and triggers these ATMMs to shake their internal weights in a way that’s 180 degrees out of phase with the engine’s unwanted vibration, thus canceling it out and yielding a smooth experience for occupants. This concept is called destructive interference, and it requires tweaking to the ATMMs depending upon the frame length.
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