Strange ring, no prompts on screen.

[sclowcountryguy]

Ok just a few minutes before posting this I heard a strange ringing like noise and actually was not sure where it was coming from being that I had never heard this sound or ring tone before. I listened for the sound and it lead me to my Android phone laying on the kitchen counter. I looked at the screen and it did not show any incoming calls or anything else that would indicate why it was making this noise. I had just got through texting a friend right before this happened and had walked away from the phone.

So what I am wondering here is why the odd ringtone that is not even one of my phones ringtones?? Was this maybe a hack or from an app in my phone?? Any ideas?