Hi JamesyJam
You've mentioned the V6 box, but posted in the 360 forum.
If you do have a 360 then check the 360 sound settings
For Sound issues go to Setting > Audio & Video > Audio Output > there are options > Follow Content, PCM 5.1 (HDMI only), and PCM 2.0
Choose whether you want the audio output to follow the quality of the original content (Dolby Digital where available) or to be converted to PCM 2.0 (stereo) or PCM 5.1 (uncompressed multi channel sound). Using PCM settings may resolve audio sync issues. Netflix will always use Follow Content. Use 'Follow Content' for any bitstream audio like Atmos where it's available on content.
If you are using a sound bar try connecting the 360 to a TV HDMI port without ARC. If you are connected to a HDMI ARC connector on the TV try connecting to a non ARC HDMI connector, using ARC has been a problem for some people. Also if you are using fibre optic straight from the 360 to your sound bar then set Dolby to Follow Content.
Also look under Settings > Audio & Video > Match frame rate > This can be set to off or on. Try turning it off/on. It's normally used to prevent blank screens appearing when the box switches between resolution formats, but can also help prevent sound dropouts