I have a 80 ft. well. It has been drawing a small amount of very fine sand all along. Now it is pulling sand a silt fairly heavy to the point of the water being discolored. It holds pressure as long as the water isn't on but when I turn on water, the pressure switch constantly clicks on and off the entire time. It burned out the 40/60 pressure switch. I replaced it with a 30/50 and it still constantly clicks the points on and off. Help!