MikeHalloran, you just described my EE senior design project! I made 3 receivers, collected delay data from them and triangulated a position. The idea was to locate someone with a "panic buzzer" using sensors on the blue light emergency call poles in many campuses.
The implementaiton of "listening" to a buzzer and timing it to within a few milliseconds proved to be harder than I thought, but I did it! I used a tight bandpass filter to listen for the sound, and measure the time difference between the RF and the sound. But that didn't work very well...
So I repeated the RF and sound at about 2 Hz. I then took my magnitude output signal from the bandpass filter and bandpass filtered that at 2Hz. After a few itterations it gave resonable results. We ended up with a map of campus and a dot following around a person with a very annoying buzzer. Accurate to maybe 5 or 10 meters. We Won best overall project from the IEEE.