No problem. As I said, I use Freecorder 4 to record from internet. It works quite well once you get used to it as it is not totally intuitive. It is a free download from the site I posted earlier.
I don't record from Youtube very much but I can't recall not being able to get the sound. I am on V4 at the moment and the only 'funny' I have found is that I have to switch recorder on before starting the source. If I do it the other way round it does not record.