Keeping the power turned on to the icemaker(s) before the water line is connected can damage the icemaker(s).
You will hear the sound of ice dropping into the bin(s) and water running in the pipes as the icemaker(s) refills.
The icemaker water valve buzzes as the icemaker(s) fills with water. If the icemaker(s) is turned on, it will buzz even if it has not yet been hooked up to water.
To stop the buzzing:
Turn the icemaker(s) off by referring to Control Panel in the Operation section.