So I recently noticed a Google Voice email (2 of them actually) in my inbox, and I checked it out. It appeared that it was from a caller I didn't know, and the messages had no sound in them. Although, in the first one sent, I heard a few phone noises (like it was a mic moving).
These are the messages:

Does anyone know what this is or can trace what it is to the source? I don't want random people sending stuff to my inbox, that could be dangerous or scary.