reply to Jeffrey
Re: Water Hammer: Possible Causes? What you experienced is the type of water hammer known as hydraulic shock. The cause was the water valve in the washer slamming shut. This causes the energy of the water to be instantly dead headed, and it dissipates it's energy in all other directions. This is quite common, especially on washing machines. But it can happen if you slap a faucet off very fast, or even some toilet valves as well. Why it was not happening until a certain point in time is beyond me. Though you may have a failing pressure reducing valve. You may consider check your home's water pressure. I don't know how a piercing valve would cause the issue.