Linking to youtube muted - is there something like "&volume=0"?

As Hugo said already you cant find an option to mute in the known parameters website, but if you will use the mute parameter it will still work.

muted:

https://www.youtube.com/embed/xY2W1As-Plo?mute=1;autoplay=1

unmuted:

https://www.youtube.com/embed/xY2W1As-Plo?mute=0;autoplay=1

You don't have that option available as parameter on YouTube. Take a look at the available parameters here :

https://developers.google.com/youtube/player_parameters#Parameters