It refers to default sounds via a full path (e.g. C:\Program Files (x86)\Spark\resources\sounds\outgoing.wav). So if a user moves his profile to a new system (e.g. from 64-bit to 32-bit or vise verse), sounds will stop working. Maybe it is better to use relative paths, and maybe extract sounds to user's profile like it is done with plugins and emoticons.
There is also a bell sound, which is probably intended to use with a buzz feature, but is not used anywhere.