Did you remove the rotors/hubs and inspect the inner and outer bearings?
Do you have Auto or Manual locking hubs?
The popping is something binding up and then releasing, this could be bearings but usual bearing issue is hum noise not pop.
Locking hubs can pop as can the u-joints on the front axle, these are not used unless the hubs are locked, but if hubs are locking without your knowledge then they could pop and put drag that wheel
Lower ball joint could be the issue as well but you probably would have noticed extreme tire wear on that side.
Here is a good read on your front axle: The Ford Ranger Dana 28 & Dana 35 Front 4x4 Axle
You should have the Dana 35 in a '97 4x4 with 4.0l engine
There are also attachment points that could be loose but the "popping" would be during braking or accelerating in most cases.
Since you say the passenger side drags(right wheel???), focus on that but when problem is found check and replace the same parts on opposite side.