After installing lawn sprinklers there is knocking/tapping/ ticking noise whenever the water runs. At any time of the day. Sprinklers, washing maching, toilet, shower, etc. all cause this noise. (All not running at the same time.) The noise seems to be coming from the main line just after the meter (behind a wall, of course.) It's a "newer" house, 15years old. I've searched other threads and they are related to hot water pipes, radiators or remodeled homes, none of which apply. Any ideas?