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O.k then very often the cable box will have a function/option to sync video and sound and so should your tv but sony Australia seem to hide their manuals pretty deep , (still looking for it) .
Not sure if the foxtel boxes are the same as north American cable boxes but I can tell you that it is common here with cable boxes and usually a reboot will do the trick.
Try this ;
Pull the cable box`s power cord off the wall outlet (cable box only) for a minute.In the mean time turn off the tv and turn it back on only after you plug back the cable box power cord.Note that it may take a couple of minutes for the cable box to reboot after you plug it back ,just give it time.
See if that helps
O.k then , was waiting for your reply and I can tell you that so far nothing in your TV's manual seem to deal with that problem but from experience you won`t need that anyway , the reboot will do it