4X4 Question: I had a break job done.

4x4 Question:
I had a break job done apprx 2 years ago and about a month after the right front wheel started making a light grinding noise for a short time and then stopped. This was in Jan. Took it back and they could not find anything that (they) thought would cause it and after a time it stopped doing it.
The following year it started again in earnest so I took somewhere else. This was around Feb. They replaced a part in the hub to the tune of $700.00. And said it was trying to engage or something like that and it ground some teeth down, problem fixed, no more noise that year.
When it started again this year, Jan I took it to the same place and they said after a day of inspection that they needed to replace a solinoid in the vacuum line that was letting water in and freezing ie. The problem. They said it was a Ford update. It stopped for about a week or two until it got into the teens overnight and it started again.
I have tried to explain this as best I can and as of today this is where it stands:
1. This only happens when it is cold ( it's 24 today and it was doing it)
2. When it starts, usually in the morning, shifting into 4 wheel makes the noise stop instantly.I thought exercising the 4 wheel function would keep whatever is sticking moving because it does not get used all that often in Chicago lately
I'm not sure who I can go to any more for a straight answer but this must be fixed, I think I am getting an ulcer from this. Also, when I called a local Ford dealer for information on the problem they said there is a servo in the hub that might be the problem, and by the way that part is about $1100.00.
I'm lost now and don't know what to do next, ANY help on the situation would be appreciated
Thank you very much for your time
Larry Steinbach