WTF of the month award goes to:

mysterious voice inside car! Rescuers save 18 month old baby hear woman's voice crying help -
but the woman was already dead! My theory is she looked dead but was still barely alive up until the last few seconds of freeing the child. Still, all of the rescuers heard the same thing.

http://www.foxnews.com/us/2015/03/1...pushed-them-to-rescue-toddler-trapped-inside/

Probably a passing dolphin.

Comments from people reading news articles about it say maybe it was an Onstar voice.
I don't have Onstar - would this make sense?

A passerby calling for help maybe?

Not from inside the car. Unless it was David Blain the magician. The car was upside down in water for 14 hours, so most likely
not a lot of people around either.