I Have a 06 F-150 FX4 with 80K on it and I'm having a problem with what seems like the 4 wheel drive dropping in while i'm driving. I'll be driveing along and all of a sudden it starts to grind and I feel a bit of a tug in the front end.
The first few times It happened I'd pull off the highway and slow down almost to a stop and then with a thud it would stop. After this happened a few times and I had a feeling it had to do with the transfer case when it would start to grind I moved the selector to engage the 4X4 and that would stop the grinding then I take it out of 4X4 and it would be ok for a while.

Has any one else experienced this?

 

It sounds like the exact same problem that I am having. From that replies that I have received, it sounds like the IWE solenoid dropping vacuum pressure and allowing the hubs to engage.