I'm deciding whether or not to extend the license so I can gain access to the new version of vBshout. I've installed the free version, but can't see where the customisable sounds are as mentioned in the feature list.
You have to turn off HTML5 sounds via vBulletin Options.
It's strongly not recommended to use custom sounds due to browser incompatibilities. All your users will be forced to install the QuickTime plugin, and even then it doesn't work on some systems.
You might be better off creating a .ogg file yourself via a sound editing program and use that instead