Axles or U-joints???

I started a thread about my axles clicking and what ones to buy but i started thinking that my u-joints in my prop shaft are shot too, well the rear one by my foot anyway, so im wondering if maybe the clicking im hearing could just be the u-joints or if its defiantly the axles, im not home now to check it out but has anyone had that happen that it was just u-joints and not the axles, i would hate to buy new axles and it not be the issue.