OSX loud siren that starts every 1-5 minutes? This one is very odd. My 2010 Macbook Air running latest Mavericks was working very well just yesterday and today it started to play a "siren sound" (sounds a bit like warning/alarm/police siren), the sound is very long (2-4 secs.) and it starts every 1-5 minutes. Of course when it happens it unmutes all system sounds :S It's worth noting I don't have any other software that I had yesterday, it just happened like that, overnight.

What I've done to prevent it and find what's causing it:

My system sounds are off (Preferences/Sound > "Play user interface sound effects" unchecked).

All the sound notifications are off. I also turned on "Do not disturb mode".

I ran Apple Hardware Test (for now the basic one, I will run the long one this evening as I'm at work right now) and it returned no problems.

Also I've installed SoundBunny to see what's the source of the sound - it doesn't show anything when the siren starts, like it's not software-related (by the way do I really need a software for this task in OSX? it's been in Windows for ages :/)

I've been restarting my Macbook all morning and once the siren started BEFORE I even log in to my account (woot?).

I've checked all the Apple beep codes, but none of them seems to be what I'm hearing (by the way are they recorded somewhere? I'd love to hear them all out and see if I can recognise the one I'm hearing).

HELP ME PLEASE, I can't work :(
Does anyone else have access to your iCloud account?  If they do, they can play a loud noise using Find My Mac.  If you've recently received an email notifying you that someone has signed into your iCloud account using a web browser, that would be an excellent sign that the Find My Mac siren is what you're hearing.

Another possibility: Did you install Prey Project on your Mac? It's a piece of software similar to Find My Mac, and it can produce a very loud siren noise.  Check your Prey account settings; if someone else has access to the account, they can play a siren noise.