It's the valve doing it's job. Sometimes the mount gets jiggered and the movement of the hydraulic fluid through the valve resonates on the mounting and body. Strictly speaking it's physics, not something to be "fixed'. Proper mounting and damping helps. If your valve is very noisy, even with some rubber (I just put some rolled up rubber bands under mine) then you can remove it and pull it apart carefully and clean it (mine looked spotless inside but did seem quieter once reassembled). I got mine back in and working, it is a straightforward solenoid valve, but be methodical and don't take to it with vise grips and a hammer is all. The surfaces of the cylinder and the piston are close tolerances to manage the fluid pressure, you don't want to scratch it up.
Bulldogger
