You might want to get him checked by a vet or specialist. Have them do an MRI or some kind of brain scan to rule out tumors. Is he current on all of his vaccinations: rabies, distemper?
If he checks out clear of any medical problems, try having him evaluated by a professional behaviorist.

A few of my dogs while in there cages will bark and growl at my relatives that come for a visit when they haven't been there for a while, but the minute we let them out of the cage it's a totally different personality.