Throughout the day/night when there is nothing playing on my Digi+ Pro/HifiberryOS/Raspi4 I'll hear the relays on my Schiit Bifrost 2 "click" every 30-60minutes. It only happens if the Bifrost input is selected to be coax for the Digi+ Pro and it is connected via coax to the Digi+ Pro.
Running the latest version of HifiberryOS.