Loud noise when return pump off

[Alexpark911]

Everytime I turn off my return pump… it make really loud banging noise like water is back flowing but vibrating at the same time… anyone know how I can fix that? This is how my pipe is setup

 

[Rmckoy]

Is there a check valve or directional flow valve in the return line ?

 

[Alexpark911]

Yes I do… you can’t really see it but I have check valve right above the return pump… and I can literally see it flopping with that rattling noise as water trickle down…