Re: 2002-2004 exploroer rear differintial whine
Well, I can't quite tell from the information given what your exact problem is.
Generally a rear end noise is caused by a bearing going out.
Axles have for quite some time now been made of aluminum housings with hardened steel internals. The 8.8 ford axle in particular is one of the best around (so good that many Jeep enthusiasts use the 8.8 when building trail riders).
I do not think the different heat/expansion properties of these materials is causing your troubles. it is possible that your axle housing has been damaged to the point that premature wear is occurring on the internals however.
If you are certain that (after a rebuild) the rear end is still having repeated problems, I suggest replacing the entire housing and assembly. this is about the same price as paying for a full labor rebuild. Actually, the one you get will likely be rebuilt from an old core unit.
Just a thought, good luck.