Jecod/jebao Knocking and hammering noise

[Arowana718]

Anyone know why I get this knocking/hammering noise when I turn off pump? Its got check valve

 

[Sassafras]

Does the noise continue indefinitely or does it quit after a period of time? It sounds like water may be draining back through the pump and check valve.

 

[Arowana718]

Does not stop, 15-20 mins still making noise.

Does the noise continue indefinitely or does it quit after a period of time? It sounds like water may be draining back through the pump and check valve.