Hi!
I experienced similar issue. It is related to rdac and I tried to fix it by Arcam service but they told me its cheaper to buy new one…
But there is another solution, I assume the issue occurs when you are connecting rdac by USB. There is no such problem with toslink or coax.
What I did was bought hifiberry digi which has got COAX+TOSLINK and then connect rdac another way. ALthough the issue still occurs when I play hi-res tracks I dont experience it anymore while playing 44Hz 16bit tracks. Its also worth mentioning that the sound quality improved after switching to COAX. Guess the cheapest hifiberry digi would be fine, and its easy to setup with volumio (another audiophile OS’es as well).
EDIT:
Oh I forgot about spotify issues which brought me to this forum. For now there is problem with spotify connect playback, there is no sound and spotify can not connect. This is probably related to some volume issues as mentioned in topic:
https://volumio.org/forum/arcam-rdac-spotify-unable-connect-t10152.html
Cheers,
amonowy