Sound distorted on ITunes playback.
I've just noticed a slight crackling on upper frequencies - especially on playback of classical piano music.
After some experimentation it looks like the answer is either to turn off the equalizer totally - or use a simple preset like bass boost that is essentially flat in the upper frequencies (recommended).
BTW not much point playing with the other settings for playback 'enhance' and 'soundcheck' since these dont seem to have any significant effect on the intermittent 'crackle'.
Enjoy!