I did about an hour long recording from my car in the Ruby Tuesday parking lot while having dinner on the assumption the signal was coming from a coaster alert system in the restaurant. Turns out they don't use these, so once again I was left clueless... until I discovered a voice message on 467.75. "Customer needs loading assistance at the front end." The first place that came to mind was Home Depot given what methusaleh suggested. The store is pretty much exactly a two mile vector from my position. which is the strongest point of the signal along the highway. This checks out, as it is the apex of the signal arc. I know about what places the signal attenuates to nothing (Arby's and the square), and out of curiosity drew a circle around Home Depot on the map to see if the position of this arc makes sense.
And it does. Based on the mean center of my circle, the actual location is very close! I think I finally have something here. I've attached the sketch and message.
