Do you experience problems during downloading?
Check your connection in Status and Interface settings window.
Use Test Server in Config > Servers.
We will probably ask you to do a test using only basic settings.
Do you experience problems during repair or unpacking?
Enable +Debug logging in the Status and Interface settings window and share the relevant parts of the log here using [ code ] sections.
I did a clean install of Mavericks and got the latest sabnzbd that has mavericks support and the sound for notifications does not work there either.
EDIT. I went back a few builds of Sabnzbd and found earlier versions do not make a sound notification either. I also tested with Elcap and Yosemite. Although Sabnzbd successfully ads it self to the Notifications list in OSX, the sound option does not work.