V6 sound issues

Hi, I'm having the same problem with my V6 box, it's fine if I select "Dolby to PCM" but if I choose Dolby Digital I get the sound cutting out for 1 or 2 seconds every 20 to 30 mins.I started to get the problem a few months ago, I assumed the box was starting to fail, the box did eventually fail a few weeks ago, an engineer came out and installed a new v6 box but unfortunately the sound problem is still there, not sure if it is happening on recordings or streaming as I don't watch recorded tv very often.

Any help gratefully received