[UKjohnnycobra]

I had exactly the same problem. A vibration from the back of the car between 60 and 65mph. Balancing did not solve the problem. The problem was, as suggested above, that one of the rear tires was out of round. The rim was fine, it was the tire that was causing the vibration. I had the tire trued at a local place in Stamford Ct and now it is driving like a new car. Problem solved for $30.

Bob in CT suggested this was the problem and he was right.