Thanks for your post duncana59, and I'm sorry to hear of the blip with both sound and picture on your V6 box.
Can you tell me if you've been able to try an alternative HDMI port on the back of the TV? Or have you possibly tried a new HDMI cable altogether?
If you can also check the connections running into the back of the set top box and at the white box on the inside of the property, that would be welcome
It may also be worth seeing if the fault re-occurs when connected to an alternative TV set, is this possible?
Kindest regards,
David_Bn