I just went through the EXACT same thing with my 2008 Limited AWD. After 9 almost 10 weeks at Ford garage here is what happened......I put 4 new (so I thought) tires on. ( I bought 2 brand new on eBay and 2 from a friend of a friend who told me they had less 5,000 miles on them. They are 22” tires and expensive so I thought I was saving close to a thousand bucks), drove down the road a mile and felt a real hard slam, then the grinding noise. Took it back to the shop tagged installed the tires and they could find any problems. Drove it back home and looked over everything.....vacuumed leaks, bearing play, bad u-joints, transfer case and differential leaks etc. There was visibly nothing wrong. So I tore the whole front end apart minus the axle tube and replaced everything; CV shaft, hub
assembly, hub actuator etc. Put everything back together and in less than 3 blocks from my driveway the same hard slam proceeded by the grinding noise. I called a tow truck and sent it to. Ford garage. They checked all ECU wiring, went through transfer case as well as differential and transmission. They troubleshooted every possible scenario on that truck instead of just throwing parts at it like most other shops do. Here’s what they found: my rear wheels were spinning 1mph faster than my fronts, but they couldn’t figure out why. So the service manager had them put 4 new wheels and tires off of a brand new F150 on the lot. They installed them, took off down the road, no hard slamming. No grinding noise. Nothing. So they checked the circumference of the tires that I just had installed ( by a different shop) and the rear tires were 1/12th of an inch smaller than the fronts. This was causing the computer to think that the rear wheels were spinning, therefore causing the hubs to engage!!!! $2400, 4 brand new Bridgestone tires later, problem solved. Tire circumference.

 

The front end is full time locked on the AWD trucks, all coupling is done through the BW TOD. You can remove the front driveshaft if needed and it will function like a RWD with no errors. As the above found tire circumference and tire pressure are key to the system not destroying itself. In 2012 the issue was addressed with a much better TOD unit. The good news is these units are very easy to rebuild and repair. A full replacement shouldn't be needed as long as the oil pump didn't eat the case.

 

Still waiting to hear if you FOR SURE have IWEs up front!
If not, pull the front driveshaft.
The front wheels will not receive any power (weather in A4WD or 4x4).
If the GEM determines that the TOD clutch needs to be engaged, the clutch will only have to spin the front stub shaft of the transfer case. It should be able to do that without making any noise.
After you rebuild the TOD clutch in the transfer case, just reinstall the front DS.

 

Not Shute if there are iwe up front from the outside looks like it and if they are there then they are on full time seen as there is no vacuum on them .
I just pulled the plug ( wiring) on the TOD so not it won’t engage when the back wheels ( computer) feels slip
this will d
have to do for now until I get the parts for a rebuild ( finding it difficult to get the right parts , and need to be certain they ar3 right because i have to get them shipped in from the USA )