The vacuum lines that had the leaks were the ones that were right behind the battery. I had taken the Expedition to two other shops (one being a Ford dealer). The first thought it was the material inside the catalytic converter rattling around, and the Ford dealer said they couldn't find the source of the noise, but wanted to open up the top end of the engine to look in the valve train (to the tune of $1,400.00). Looking in this forum as well as in some F-150 forums (plus switching the vehicle from Auto4WD to 2WD and back really narrowed it down to either the vacuum lines or the wheel actuators. Two hours after dropping the Expy off at the 3rd shop and it was diagnosed and fixed (for $156.00).