Topic: Spike/Dropout on Playback only

Hi
My audio set up is 2x HDSP9652 (synced together via word clock)  and an SSL Alphalink Madi AX(24 Channel Analogue to ADAT Convertor) I have One of the HDSP cards as MASTER linked via ADAT to the Alphalink (which is slaved to HDSP9652 ADat 1.) As mentioned before, my 2nd HDSP9652 is word clock slaved to Card 1 (and terminated.) which is used in conjuction with analogue expantion In/Out(Ai-8/Ao-8)
      Everything  shows correct sync etc.,  The problem occurs  on playback only(record is no problem)  It seems that sync is lost momentarily at random intervals ( then re-syncs.) with total audio dropout( and large audible CLICK)
I have tried various buffer settings without  succsess and dont know what to try next.  Any suggestions and advice on a solution to this would be most appreciated.
thanks in advance
Mike Dixon
(System -PC Intell Dual core)