@trabicki with a standard button/chime configuration, the circuit is only closed when the button is pressed. This generally works out to mean that the chime works even if it requires 16V, and the transformer is pushing out 18V or 24V. Some people with lighted buttons have run into this issue when the light on the button burns out at a faster than usual pace.
With the Greet, since it is powered on all of the time, the circuit is complete all of the time. In order for there to be silence at the chime, the Greet has to “Use” all of the power. This means that the resistance provided by the chime needs to be pretty exact. A chime that requires 16V with a transformer that pushes out 18V will have a buzz sound, this is because the chime is not incorporating enough resistance at 18V.