Listen to it or record it, then listen for street names, call signs, names of towns, cities, counties. If you can get a city or a county, Google the name with the frequency. Example- 39.980 Custer County. This is the only way. You can get a general idea of where it is coming from if they give a time (time zone) or if they have an accent (NY/NJ). So get a pen and paper and get ready to start writing what you hear then Google it!