Apple Music from within the Sonos app has no crackle/clip, it only occurs when using audio from video source. I'm using a matrix to connect to a projector, with the Sonos-provided optical adapter for the signal to the Arc, HDMI cable is 4K.
I’m still within the return window on the Sonos products, so if in all these posts and years NO ONE has found a definitive solution to this highly common problem, they are sadly going back. Great sound for music, but the point was to be the theater sound system.