What Secondjeremy said.
There is a top hat shaped steel cover on the front of the transfer box, that had rusted internally and was stopping the free movement on a Series 3 I pick up. You can get it out from underneath but it is so much easier to remove the drivers floor plate, plus you can see better.
HTH
A friend had something similar.
Replacing his engine mount rubbers with new ones stopped it.
He replaced them with Ford Pinto ones as they are a little bit taller so he also got better clearance on the front pulley.
HTH