Recently, Facebook introduced notification sounds.
This is what popularity sounds like in 2013.
But there's a hidden Easter egg within...
It's actually this chord: the Fmaj7.
The first note is F.
Then A.
Then C.
Then E.
Which is to say...
Consider our minds very gently blown.
The full story: Facebook's audio designer answers "How much research has gone into developing the Facebook ping sound?"
quora.com
It's also based on international ring tones — and the doorbell-like sound of someone calling "LASSIE!"