Grunting or growling is one of the snorting rabbit vocal sounds that this pet may use to try to speak to you, to other rabbits or pets. Like snorting, hissing, screaming, squeaking, and so on, it is one of the unhappy sounds that these pets make.
Why rabbits grunt or growl
If your bunny grunts, you need to be very careful as it may attack you afterward. Do a quick check on the reasons why he or she grunted. This will help you to effectively interpret what this pet is trying to tell you. Some of the scenarios when a bunny may growl include the following:
Angry or stressed
More often than ever, grunting is a sign of anger or irritation, i.e., your rabbit is trying to tell you that he or she is irritated, upset or maybe something is hurting him. When it happens, you need to watch out. If not, it will lunge and attack you.
Your bunny may be sending messages such as ‘get off my back’, ‘leave me alone’, ‘be careful’, or ‘get out of my way’ and so on depending on what you did.
This pet may growl to show disapproval to something you have done. For instance, if you try to hold or carry it from the ground and it doesn’t want it may grunt. Also if you take its treat away or pet it improperly, you may hear this sound. Your furry friend is trying to tell you things such as ‘leave me alone’ or ‘stop it’.
All you need to do is to stop doing whatever you did before it grunted, otherwise, it may nip or bite or attack you if you do not heed to what it is trying to tell you.
As a warning
This sound can also be used as a warning, especially for territorial rabbits. They are asking you or other rabbits to ‘back-off’ their territory in case you or other bunnies are trying to invade it.
During courtship, these vocal rabbit sound may try to warn their partner such as ‘not now please’, ‘I do not feel so hot’ and so on. 
As a sexual behavior
This may also be interpreted as a “noise of sexual arousal made while running around the prospective mate. It may also involve thumping and wild tail waving”.
Afraid or scared
Finally, startling your bunny, rapid unpredictable movements, sight or smell of a nearby prey may cause fear and make your rabbit growl. Also, some may grunt when they feel cornered.
Sign of love
Whereas this sound is often associated with an unhappy bunny, it could also be a sign of love if your bunny grunts around you softly. 
When interpreting a rabbit’s body language as well as some of its vocal cues you need to consider what is happening around it. If you hear this sound, consider leaving it alone or checking if something is hurting it.
Also, one rabbit may communicate in a slightly different manner from another. For instance, some may grunt when they are in pain while others will grind their teeth.