It's still a beta version of the IM.
Look at the sticky:
http://forums.d2jsp.org/topic.php?t=39800276&f=28&v=1- You CANNOT disable sounds at this time. I will add a SETTINGS window at some point to control this (top left icon), but this is not yet available.
- There will NOT be any public channels! People NOT in your guild will not be able to join your guild chat.
This answers your questions.
Sound will be fixed, but not right now, and njaguar has no plans to make it "public". It's a conversation with 1 friend at a time, or with your whole guild.