Strange, I have faded AudioStreamPlayer's by adjusting their volume DB in the editor and haven't had any issues with cracks and pop sounds. With the AnimationPlayer, are you just adding a keyframe with the volume_db property?
I've had issues with cracking and popping in Godot if the audio has too much bass or tremble, where it would exceed the buffer limit, but not when fading. It might be the buffer is having an issue when fading the audio out. I don't remember right off what I did to fix it in Godot though. I think one way I fixed it was normalizing the audio and then just increase the volume_db of the AudioStreamPlayer node. This made the audio file itself have a lower range, but because of the increase in volume_db, it sounded almost exactly the same and avoided the popping sounds.
I think that is what I did, it's been awhile since I've had the audio issue so I may be misremembering :sweat_smile:
