my kids never growl or snap at one another because i would never allow it. they play growl when they are running around but even then, if i think it might be getting out of hand, i clap my hands or make a loud sound to distract them
this is JMO but i would definitely address this and stay on top of it now so you can get rid of any potential aggression. probably what i would do is if i heard one of them mean growl at the other (for any reason, even over a toy), i would pick them up, put their face very close to mine and calmly but in a very serious manner, say "no."
i will not stand for any type of aggression in any of my kids. none of my kids have problems with food aggression or play aggression or toy aggression. two of them started fighting over a toy earlier in the week (it was not even really aggressive fighting) and i broke that up REAL fast.
hope that helps a little bit!
and again all of this is JMO
