I've installed a new Fluidmaster 400C fill valve that is working, but now I've got a small leak. The water in the tank drips just a little bit, which didn't used to happen, and the fill valve makes a quiet humming sound when it doesn't need to, like it wants to work even when it hasn't been flushed. I've shut off the water valve to avoid having standing water after a while. Many thanks for your help~!

Where is the leak?

Where tank is full, is water 1/2'' below overflow pipe?

After installing the fill valve did you clear it of debris according to install instructions?

Chuck