@CMAldrich, I have not spent much time troubleshooting this problem since I posted my message, but I am going to look more carefully at what is unique about that area. For one thing, there is a railroad crossing about 150 Yds furter down the road (but that is not the trigger point) and there are high voltage power lines nearby. When traffic is light, I'm going to creep along and find the exact trigger point. Maybe then I'll have a better clue as to the source. Incidentally, I have a very sensitive radar detector in the car, and it never makes a peep in that area (unless there is a speed trap set up).
Let me know if you isolate the source and I'll do the same.
Cruise_2_xs