DANTE Network with X32, 2 M32's and a D400 Aviom Switch- Audio Popping


We have two venues linked to a single broadcast room via an isolated network that supports both DANTE and NDI traffic.  Despite DANTE Controller not showing any clock errors, we get popping artifacts in the audio stream on the output side of the DANTE network.  The diagram shows the layout of our network. 

Originally we started using DANTE with a single M32 networked to the MacBook Pro running DVS.  That setup by itself would cause pops to be heard, but again no clock issues showed up in Dante.  

Anytime we try to set either M32 to sync to external, we start having loud pops in the PA as the clock sync with the DL32's gets messed up.  Enabling sync to external in Dante Controller sorta works for a bit, but will ultimately cause clock failure as well.  THe most stable config seems to be M32's sync internally, X32 producer set to sync to external and letting Dante Controller sort out the clock master.  I should also point out that we are using shielded cable from M32 to DL32.  We even took the DL32 out of the link in venue #2 to see if it made a difference and it did not.  

I can't seem to find anyone else with similar issues.  Any google-fu with M32/X32 and popping only leads to the STP issue which is not our problem.  Also, the NDI equipment was added, but the popping problems existed prior to the addition of that hardware to our network.