Awhile back, mine was making a noise, as if the IWE on one side or the other wasn't fully disengaging. Could hear an occasional clunk and a feeling of a binding, dragging sort of.
Since I've had close to a half dozen Explorers over the years and even a Ranger, I did some digging here, read about the IWE stuff, vacuum, etc (none of which the AWD Exploders have, but..) to me the noise sounded a good bit like a hub on an Explorer when it starts getting bad. It makes a hum, has a little vibration. So I checked my hubs...and they both were starting to go. Replaced 'em, and no more issues. Also, now that binding feeling and sound is gone. When I did notice it before, it would only ever do it in 2H, in 4A it wasn't there.
Now, I'm not going to get into another endless debate about the merits of when and how to to use 4A, but I can say this, I'm 100% comfortable with using it as needed in any condition.
I grew up driving a Jeep with a points ignition, manual hubs, two sticks through the floorboard, and power brakes? What the hell were those!? Point is...the system used in the Expedition is a little more advanced, it's been engineered to be used on an as needed basis, and if Ford deemed it unwise or unsafe to use 4A they'd have disclaimers against it in the book and probably on the visor. Yeah, it'll cause a little more wear, and little less MPG. But in the winter, when there's a blowing snow and slick stuff on the road, I'll trade that decreased mileage and slightly more wear against a lack of traction. Some of you guys don't have blizzards, ice, or mud. Some of you do. Thankfully we have good stuff under us to get through, around, and over it all.
What's even cooler than 3 tons of dry ice? Using my Expy in 4L to drag a tractor out of a barn. Tractor (9N) had been sitting for years, clutch is stuck, so even in neutral it won't roll. We took the plugs out, soaked the cyls with diesel, let er sit for a day, then I hooked up and brought 'er out to daylight. At first it dragged, then it got loose and rolled. Ford...saving a Ford. Gotta love it.
Expedition moved it like it wasn't even there. Doubt my Explorer would have moved it though, and it's a V8 too. (weight, traction is the issue with it).