Bluesound Node to Cambridge CXA-60 issue

Looking for some suggestions.  My son has a Cambridge CXA-60 integrated amp.  He's streaming with a Bluesound Node N130.  The Cambridge only has coaxial and optical digital inputs (no USB).  My son noticed that there is a faint clicking sound when using the internal dac in the Cambridge.  If he uses the dac in the Node, the clicking goes away.  We've tried coaxial cables by XLO and Morrow, so I don't think it's a cable.  We have the same issue with optical (cheap cable, I don't use optical for anything).  

Any idea what the problem might be?  Any help is appreciated.