What's making this sound on my Mac? (DeliveryCompleted.aiff)
Solution 1:
Turns out it was Adium's way of telling me a new contact had signed on. I disabled the sound in Adium's preference and it's gone away.
Solution 2:
This sound most likely has nothing to do with Xcode. It is a standard sound used throughout OS X for many purposes, including installer notifications. It is also a ringtone on iOS.
Solution 3:
IIRC SoundBunny for Mac ($10, free 30-day demo available) will show you which apps have recently played sounds on your Mac.