Friggin' A, i can't believe it. Yesterday i decided to remove the rear drive shaft, regrease the splines and u-joints then re-install. While doing so i happened to glance at my transfer case. The OE skid plate had been smashed up onto the Tcase and was making contact with it. So i pulled it down and away from the Tcase. Now no more vibrations during idle. Such an easy fix, just finding it was the hard part.