4wd noise while decellerating

[st_pinetree]

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 or the vacuum actuator?

[BahamaTodd]

You were driving on the highway in 4wd?