Ford Repair: 2000 Ford Explorer 5.0 Eddie Bauer AWD Tranny/Transfer Case Troubleshooting Help, fly wheel, torque converter

Question
Recently while sitting at a red light waiting for green, I heard a loud bang (felt like truck jumped slightly) - looked in rear view to see what hit me!  Tried to accelerate & move forward - truck will not go as if in neutral but I hear a loud whining/slight grinding.  This noise can now be heard mostly while in Park & neutral - Truck will not move in reverse or any Drive gears.  This noise appears to be coming from the transfer case when I crawl under the truck.  Installed a rebuilt motor 2 hears ago - running strong - the tranny/truck has 250,000 miles to date with no prior problems.  I intend to have it fixed but need an idea where to start.  Do I pick up a used/re-built transmission & start there, or could it be the transfer case that needs to be replaced (or both) - Truth is, I'm not sure what direction to move in and need help troubleshooting this problem in case the problem is with neither or both!!  Help!!

Answer
you had either of two things happen. either the clutch inside the transfer case broke or the fly wheel broke !!!. ( the gear the starter hits to turn engine over and connects  the engine to the transission torque converter. this was not an uncommon. problem. very easy to check this though. you can either jack up vehicle or just crawl under. looking at where the engine and trans bolts together driver's side you should see a black plug about the size of a hockey puck. you should be able to see the fly wheel spining. if not, that's the problem