Both my Ziggy and RB Starr would growl over their food too. They were very food aggressive. Starr eventually out grew it but if one of my other cats gets too close to Ziggy while she's eating she'll start growling. She'll also try to steal my other cats food so I really have to watch her.

She also growls and hisses if one of my other cats keeps chasing her or gets too close to her when she just wants to be alone. When Ziggy and Pearl were kittens they both growled at the vet. It was so funny to hear wee little kittens trying to scare the vet. Hopefully your cat will out grow this.