just a little bit of info that may or may not help someone. set up new box and line added, picture wasn't jumping however i felt the sound was jumping ever so slightly at times, spent some time messing with softcam and decided to get a 2nd line from different provider, low and behold it was still doing in, I was convinced the lines at this point weren't the issue, went into ac3 downmix settings and turned it on - not only is the sound louder from the box, the issue appears to have sorted itself now. just a coincidence - im not sure but may help someone...