I was trying out the new snapshot to see if the issue where I was quite in stream and system sounds were even more quiet has been fixed. At least Now the sounds were fixed, but every sound would loop in the stream. My voice, my game, skype and even music from windows media player.
Here is a list to my channels past broadcasts. Look at the videos titled "Fixing sound issues?"
http://www.twitch.tv/aaartis2/profile/pastBroadcasts
MC-40924
Looping sound on stream
Resolved
Invalid
0
(Unassigned)
Unconfirmed
loop, looping, sound, sounds, stream, streaming
Minecraft 13w48a
Retrieved
I had the same problem but i fixed this by having my twitch stream muted in the browser. The cause of this loop is if you have system sounds enabled and you are watching your own stream Minecraft will be taking all sounds from your computer including from your browser and therefore streaming those sounds. If this isn't very easy to understand I am sorry, someone else could probably word this better but I hope this helps you! ~Rhino