How can I prevent my Mac from periodically whooshing at me? Seemingly randomly throughout the day, my mac will "whoosh" at me.  I set up Messages, but whenever I switch to Messages after the whoosh, I don't have any new messages and usually my buddies are set to Away status anyway.

Notification center is empty with "No new notifications."

I don't have the mail client set up or running, so it can't be that.  I do use Reminders and sometimes put things in the calendar, but I don't think those are whooshing at me.

What is whooshing at me and how do I make it stop?
Could it be the sound alerts Messages has configured by default? I'm particularly thinking about the sound when a contact comes online/goes offline, which sound like a "whoosh".

You can check and disable these sound alerts individually for each event in the Messages preferences.