I have done several searches and found multiple people with the same syptoms I am having. However no clear fixes are listed in any of the posts. Occasionally when slowing from highway speed I get an awful howl/grind noise in what sounds like the front end. Similar to the sound you would get if you picked up a piece of trash on your driveline or something. It diminishes as you slow and turns into a series of clicking sounds. If I hit the 4wd button it goes away and all is fine. From what I've read on the internet, I am thinking its a problem with the axle acuator partially engaging the axle on its own. Do I replace the vacuum switch?

 

I would be checking the wheel bearings and front half shafts. At highway speed, swerve the vehicle lightly across the entire lane and see if the pitch changes from left to right. Report back with what happens. Dont swerve dangerously, just weave back and forth. Your trying to load/unload each side of the wheel bearings. If the pitch changes while swerving, thats is most likely the culprit.