I've had this problem for several months now. I started hearing this cracking noise when I turned left of right. Only when I've driven the truck a while. I've replaced the boots from both sides and brakes and roters as well. I still have the same cracking noise coming from the bottom. Sounds like it's coming from the front differential. I have no idea what it is. Please help
You need to identify exactly where the sound is coming from. To do this, jack up the front end and put it on jack stands. If it's what I'm thinking it is, you can probably keep the tires straight, then have one person hold one tire while you turn the other.
If the noise is coming from the differential, as you are saying, you are probably going to need a new one. I am not sure if your Expedition comes with a locking front differential (as in a posi unit or whatever Ford calls it), but would assume it probably does. If the noise is occurring inside the differential, it may be that the clutches inside of it are bad and causing the noises. The noise would only occur when the two tires are spinning at different speeds. When the tires are spinning at the same speed, the differential turns as one unit and would not exhibit any noises in this case.