My MAC is running 10.7.5.. I haven't installed any software recently. It seems to happen to happen when it goes to sleep, or power save mode. No it isn't very repeatable but I will keep an eye on it. Login items are iTunes helper, adobe resource synchronizer, WD security helper, dropbox and blackberry device manager. Not much..
Currently I downloaded Intego virus software and am running a full scan.
It maybe.... but it's unlikely to be malware. Probably just an app that uses that sound to notify you of something.
But to help we're going to need some more info:
1. Which version of OSX do you have?
2. Have you installed any software recently? If so, what?
3. When does it do it?
4. Is the action repeatable?
5. Which apps do you have running and loading at start up? (See System Preferences - accounts - your user - login items)
6. Does it persist if you disconnect from the internet?[/QUOTE]