white noise when playing wav via pi-digiamp+

I’ve installed volumio 2.041 on a pi3 with an iqaudio pi-digiamp+. Works very nicely streaming web radio. However, when I try to play a 1411kbps wav (from SD or USB-attached HDD) the playback is interspersed with loud bursts of static/white noise. (the same wavs play OK on PC). Settings look OK (as per IQaudio page). Any pointers on how to diagnose the issue ? Thanks.