The solenoid is activated by AC current (50/60Hz)
Sometimes when the windings aren't winded tight enough, the coil can cause a (50/60Hz) humming noise.
This is nothing to worry about. Nothing goes wrong and nothing gets hot or can cause harm in any way.
When people tell you to replace the valve, ignore them. They are speaking in their own interest, not yours.
Greetings from Amsterdam
Frank Heuvelman, November 2019