Visual Composer Builder - YouTube Video No Sound

I am using the Visual Composer builder for WordPress - I've added a background YouTube video that plays perfectly fine, however there is no sound at all. On the demo theme the sound for the video is playing. Also another thing i have noticed is that when the video is playing you get an advert popup at the bottom of the video.

I'm wondering has anyone else come across this problem before and if so, how can it be fixed?

There is no Javascript/jQuery errors.

Site URL

Theme URL

thanks in advance

via Chebli Mohamed