General :: Odd Single Pointless Ring?

I was sleeping so wonderfully at 1:30 in the mourning when my phone rang, but the odd part is. I had no notifications, nor was I receiving any calls. To make things weirder my phone made ring that was not even set as my ringtone and wasnt even a ringtone. To describe it, it sounded like a standard digital ring with a frequency at what i could guess 750hertz and it only rang once. Another odd thing is after that it seemed to have put my phone on vibrate. What is going on?