[deano_hoosier]

I, too, have heard similar sounds from the towers/lines. First I thought it was someone who had dropped a metal skid on the ground... but we are not near any such commercial operation. What I now think it is... is the thermal contraction/expansion of the power lines due to heating of sun in day and cooling at night. The power lines have to "grow" in the heat and "contract" during cooling and this causes the lines to slide over the cable guides installed to facilitate that movement. Some of this movement gets noisy.