A deep "GRRrrrrrrrrrrrrrr" is how they growl. Mine growl in phases. Chester suddenly learned he could growl when he was about a year old and he growled at everything for about a month. I would ask him what he was doing, he would look at me and growl. Tell him company is coming... he would look at me a growl.. It was a new noise for him and he loved using it and used it a lot until it got old and he quit. Giz has learned how and a few months ago, she went through that same phase.