What is the noise I'm getting on waking up my MacAir?
Recently both my MacAir 2013 10.9.5 and my wife's Macbook 2008 10.8.5 have been making a short squeal when we wake them from sleep or restart. We've installed no new software. It's not a dvd drive--I know that sound and my Air doesn't have one anyone. We have started using Messages recently, and if we are leaving it on, could this noise be an indication of an incoming or unread message? Or something else? Thanks for your ideas.
MacBook, OS X Mavericks (10.9.5)