Q: Popping noise when I turn my 1999 ford expedition

This sounds like you may have wheel bearings that are going out. A wheel bearing will usually fail due to pitting or small damage on the surface of the rollers or the bearing race. Both the surface of the rollers and the race is precision machined to tight tolerances and highly polished to allow the rollers to pass easily over the race with the addition of bearing grease for lubrication and cooling. Over time the bearing will wear slightly, allowing microscopic pieces of metal into the grease. Bearing noise can sound a lot like a brake pad dragging or grinding. It can also sound like whirring, whining or humming depending on how much sound deadening material your vehicle has in it. Bearing noise will always be dependent on vehicle speed meaning as you speed up or slow down the noise should change frequency or loudness. Cornering may affect the noise from a damaged front wheel bearing and is usually more pronounced as you make turns. I would suggest having a professional from Your Mechanic come to your home to take a look at the car and check your wheel bearings for failure.