We recently installed an American Standard 3 Ton Heatpump system with airhandler. The indoor TX Valve occasionally produces a water hammer like sound, which last for 30 secs or so. It annoys the homeowner, certainly at night. We have replaced the TX valve, but no result. What could be the cause? The lineset is 7/8 x3/8 and is 40 ft long. Th system is charged with F22. Anyone any ideas? Thanks.