I've got no sound also. I tried to run it today and it said it couldn't update, so I had to download the .exe again. After I did, I had no sound. It's a temporary issue due to server load, I guess when you download it fresh it doesn't get the sounds, maybe because that saves on server traffic.
Multiplayer is basically the same as single player, but not all the features are there. There's monsters, but they can't hurt you and you can't hurt them. The world is generated the same, but will be the same on a specific server each time you log into it, unless the admin wipes in and loads a new world (which I doubt you can be online for). I think storage containers still don't work, not completely sure about mining materials and gathering them. The one server I logged into had a command setup so you could spawn a bunch of tools and stuff instead of having to build up to them. You also can't take any damage, at least on the server I was on.
What I didn't like about it was that people are terrible architects. I've been playing this like a medieval adventure where I build my castle and slay zombies in my quest for materials and ore. I logged into a multiplayer server and it was like some 6 year old threw a bunch of glass up in a manner that you could get inside and called it a building. Every building had tiny little rooms with makeshift stairs leading up to more tiny little rooms, effectively turning just about every building into a massive tower/3D labyrinth.
Oh, and as I came in, someone else did, and they decided to burn the place down. So as I explored and got lost in the mess, a large section of it was burning down while people bitched. I quickly realized that my solo medieval adventure was more fun, at least to me.