SOLUTION - After all that has been said I would like to suggest the most common cause of this issue. This issue will regularly occur when the charging port flex connector is replaced. In this case the crackling may be caused by a grounding problem between the top of the charging port flex connector and the metal screw panel. The top of the connector must be insulated from the screw panel that secures the ribbon cable onto the logic board. This can be accomplished with a small piece of electrical tape.
The issue may simply be caused by the light sensor. You can diagnose this by comparing the brightness of the Apple logo screen at startup and the lock screen. If the Apple logo screen has a normal brightness compared to a dim lock screen then the issue is the light sensor. To fix you simply need to remove and correctly seat the camera, speaker, and light sensor.