A cam phaser is used to adjust camshaft timing while the engine is running; it is part of the camshaft sprocket. They operate using oil pressure and are used on both the 6.2 and 3.5, as well as every other modern engine. When the engine is shut off, the cam phaser is supposed to “park” so that cam timing remains locked during the next engine start. Once oil pressure reaches the phasers, the locking pin disengages and the timing can be controlled.
A small percentage of the earlier phasers (Pre 07/18) were not built with tolerances by the supplier, which can cause them not to lock properly on engine shutdown. When the engine is restarted, the phaser makes noise until oil pressure is received, which takes a couple seconds. It does not result in engine damage, only a noise. All of the ones I’ve seen have been faulty within the 5/60 powertrain warranty so the repair cost was fully covered.
Thanks! I learn something everyday (and that's hard for me...LOL!).