let out (some sound)
To utter some loud, forceful sound. I let out a shriek when the dog suddenly jumped on me. The lion let out an intimidating roar.
growl at (someone or something)
To make a low, guttural sound or speak in this manner. We slowly backed away as the dog growled at us. The old man growled at me to get out of his yard.
growl out
To speak so that one's voice has a low, guttural tone or quality. A noun or pronoun can be used between "growl" and "out." I bolted after the old man growled out a command to get out of his yard.
growl at someone or something
to snarl at someone or something. Don't growl at me like that. The dog growled at the cat.
growl something out
to say something with a sound like growling or snarling. Jane growled a few words out. She growled out a few words and the gates opened for us.