In Find my iPhone, did you tell it to make a sound along with the message?
It's the Sonar ringtone. It plays it over and over again. Without known the size of your house; my advice, start looking before its battery dies. Maybe send it another message and double check that you tell it to play a sound along with the message.
Use igotya for added security
As near as I can tell, the igotya app that does this is NOT the one(s) on the itunes store (i.e. requires jailbrake). Is this correct?