Regarding the issue of noise from hydraulic valves
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The gas generation hydraulic valve often makes a loud humming sound when it is opened, accompanied by vibrations. For a long time, we have taken measures such as replacing the solenoid valve and lowering the oil temperature; in most cases, the noise stops temporarily after replacing the solenoid valve, but it reappears after just two shifts. In a few cases, the noise does not occur again even after replacement. We have also suspected friction issues with the cylinder and valve stem, but we did not investigate this further. Sometimes, the problem resolves on its own after some time and the noise stops. . . . . . . I hope you all can give me some advice... Thank you
The buzzing sound mentioned by the poster is likely coming from the electromagnet; the sound produced when the solenoid valve changes direction or releases pressure is not of this kind. You can try replacing just the electromagnet (there may be issues with its quality or power).