I notice no hiss, noise or pops, although I rarely notice hiss generally.
I have done a little bit more listening to the Calyx M, and comparing it against the Hugo as well as the AK120, using my JH13 Pros. The Hugo is a little smoother, particularly with high frequencies and transients. But the Calyx M has a bolder sound, with more saturated tonal colours. The Hugo sounds tonally light by comparison. The slight grain I noticed earlier has already disappeared after a few hours of playing, and the sound is noticeably filling out and deepening. This player is already sounding great. Although it's rather larger than I would have liked, with 448gb capacity and excellent sound quality this could finally be the one single box player that does it all.