Loud static with Hifiberry DAC+

I can hear the chime on startup, but playing a track results in a loud static noise. I can hear the track very faintly behind all the white noise. I have tried the instructions here https://www.hifiberry.com/guides/configuring-linux-3-18-x/ to no effect. Any clues?

Raspberry Pi 3
Hifiberry DAC+ Pro
Linux volumio 4.1.19-v7+ #851 SMP Sat Mar 5 22:58:42 GMT 2016 armv7l GNU/Linux

Seems to be intermittent. One track will play and if I change the track, nothing but static.

Updated to kernel

Linux volumio 4.1.21-v7+ #872 SMP Wed Apr 6 17:34:14 BST 2016 armv7l GNU/Linux

Seems to be playing tracks now. New problem, it switches intermittently to a kind of ‘lo-fi’, where it’s quieter and not as clear.