The TV is connected to a Sky+ HD satellite box. I also have another TV in my office connected to the same 'system' but this TV does not 'lose' sound.
Yes I tried that ....it worked for a while then the problem returned.
I don't have a DVD as the sky box allows recording. As I wrote earlier the other TV situated in my office 'holds' the sound correctly. This TV is connected to the satellite via the TV/Sky box in my other room where the sound is fading.
The TV and Sky Box are linked by a single black cylindrical cable (SCART) from 'Scart' on Sky Box to 'AV1' on the TV. The RF/Antenna link between the TV and Sky Box is a white cylindrical aerial cable...I assume that is a coax cable.