I'm plannig a similar design for my robot, NINA.
My theoretical approach is to have a ring of microphones attached to analogue-to-digital converters and measure how much voltage is received from which microphone. The microphone that returns the highest voltage is the most probable direction the sound comes from, or the robot can use a mathematical algorithm to find a "medium" in the voltage of the ring of microphones. The Robot can move toward the noise using a digital compass, encoders...whatever you see fit.
I don't know how well this would work either, though. Anyone Else?