I have an intermittent problem with my 2002 Outback wagon. Occasionally, while driving at highway speed (with cruise control on), the rear wheels "judder" vigorously (violently?)-- I feel like I am driving on the rumble strip on the side of the interstate. There is no pulling , the vehicle tracks perfectly straight. Upon pulling over to the side of the highway and shutting off the car, and starting out again, the symptom remained. So, pulled over again and shut car off, then restarted engine, the problem went away.
The previous owner (my father in law) had the same problem 4 years ago, and the dealership replaced the differential.
I realize that intermitent problems are by their nature hard to diagnose, but any advice would be greatly appreciated.
Thanks-
John