loud bang from front drivers side wheel

[youknowit]

I have a 99 ford explorer and when I engage 4wd it seems like the brake is hung up and then busts loose and hangs up again and it makes a huge bang sound. does anyone know what is wrong with it

 

[Turdle]

You are going to have to tear the front end apart.

My guess--front diff carrier bearing caps are broken inside the diff.