Clock issue in cue system .Popping
 

I have a pro tools hd 3 rig with 9.0, expansion chasis with PCIx cards.I recently upgraded my cue system to the roland reac m-48 etc... I am using presonus digimax fs units through a 192 digital interface.bnc clocking sounds horrible.I switched the digimax to adat clock and it seems to be better but still the occasional digital pop.I have checked all cables and connections.it only seems to be showing up in the d/a section.I am using the digital out of the 192 and its perfect.Any help would be greatly appreciated.