Is this on all videos or just particular ones?
Have you tried restarting your V6 via the Help & Settings menu? Choose the first option for a simple reset.
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Thanks for your post and welcome to the forums. It's great having you on board with us in the Community.
I'm sorry to hear you're having an issue with the sound on your YouTube app.
I can see that japitts has given some great advice, please give this a try and let us know how you get on.
As all other apps and channels are fine, this one may be a little complicated or could be an easy peasy fix. If restarting doesn't help - try logging out of the app and back in to see if this helps too.
Keep us posted on how things go.
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