I’m hearing what sounds like a water hammer in the pipes near my hot water heater(tank). With no water running, it knocks about every few seconds to a few minutes. I turned off the water heater at the breaker, electric only. Waited a day and used up what hot water was left. The knocking continued. I turned off the water to my house at the meter and it stopped. Turned that back on and turned off the water going to the hot water heater and it stopped. Any ideas what might be going on here?