My pet rabbit sometimes gets angry when I walk past her. She then makes a growling sound and "attacks" me.
We had her spayed and thought that this would help, but the problem still persists.
Is there a reason for this happening? Can it be treated?
Rabbits have two traits that can cause this behavior, they are very territorial and they have a strong grooming hierarchy.
I assume your rabbit enjoys getting petted, If you sit on the floor she will probably come lay next to you and let you pet her for long periods. She may also jump up on the couch or bed to spend time with you. She is the Princess and you are required to pet/groom her on demand.
If this is the case, she will likely have her head low and be in the "you should pet me now position" after "attacking" you. The fault here is yours, you have failed to recognize her superior position as the Princess and provide the grooming she demands. When passing her, you should always acknowledge her "Princess" status by bending down and giving her at least one pet.
If your rabbit is not a Princess, she may have tired of you invading Her space, she it telling you to "Get Out". Her head is probably high, ears forward (if she has stand up ears), she may box at you with her front feet.
The difference in behavior between "Princess" and "Get Out" may be subtle.
Growling. Some rabbits do growl, it is more common in the smaller rabbits, lion heads are more likely to growl then other breeds (in my opinion). It is a communication trait, it does not correlate with dog growls. It can have many meanings. We have a growling rabbit, if it has specific meaning we have not translated it yet.