Why does my cat hiss for no reason?

My cat is a very friendly cat. She doesn't bite, nip or have aggression at all. Very friendly with strangers and to my other animals (ferrets). I just find it strange that she has "attitude" sometimes for no apparent reason. If I'm out gardening with her and we go in the house she hisses. Sometimes when she is jumping down from the couch (by her own choice) I hear her hiss. Other times she'll be rubbing up on furniture (where no other animals have been in contact with) and starts purring then hisses and then goes back to petting herself. She has done this since she was a kitten and I'm almost thinking it's just a quirk but if someone has any insight please let me know.