Rabbit clucking is a vocal cue characterized by a short, guttural sound that might resemble a hen clucking, but it is softer (lower pitched) and shorter. Sometimes it might sound like a chirruping sound.
This is one of the happy and contented bunny sounds who could hear besides purring and humming.
Before we tell you what it means, this video has a rabbit clucking and it should make the sound familiar to you.
Why does my bunny cluck?
How do you decode this sound? What does it mean? Here is what the sound is most likely to mean if you hear it.
If you hear it while your bunny nibbling on some treat or food, it is an indication he or she is satisfied with the treat or food you offered. It is a sign of appreciation and this pet is trying to tell you ‘ I am satisfied’ or 'I enjoy the snack you gave me’.
Sometimes, this sound will be associated with a doe as she is feeding her kits  and it still indicates satisfaction.
Contented and happy
Besides clucking while eating, you may also hear this sound while petting your furry friend. They are trying to tell you they are contented and happy. You could also hear it as your bunny is dozing. It still indicates contentment. 
Due to the slight variation on the various sounds that a bunny might produce, it is good to always consider the circumstances under which a certain vocal cue was heard. This will ensure you interpret it correctly.