2015 RT 5.7 M6
I have an RT+ 5.7 so no active exhaust. I put my phone on record and place it next to the solenoid and it definitely clacks when I cycle the ignition. As for solenoid appearance, I pulled the image directly from the 5.7 service manual and the solenoid is on the "backside" of the image and not visible except for the electrical connection. But it is possible the illustration is wrong as the manual states the engine is a 348 in 2 spots.I think that diagram is the V6 cam phaser solenoid.
The V8 solenoid looks different (pic attached). It inserts into the front top of the block, above the front cam bearing.
The clack sound may be the TB butterfly doing a self-test to determine it moves through its operating range.
On the '15+ active exhaust system, the AES valves also go through a self test and go through their range when the ignition is first powered up.