Solenoid humming

[AdamCz]

Got a GHL solenoid a few months back to control my water in my ATO bucket. Have noticed it recently that it sometimes hums when it switches on. If i turn it off and on again it sometimes hums and sometimes will stop. When humming it doesn't appear to be working (water is not flowing). Any idea what the cause might be and how to fix it?

[GHL Support]

Please note that our solenoid valve is only suited for CO², not for water.