My dogs and my cat burble in their sleep. The cat also does an "urr" and an "eh, eh!"
The urr is the noise he normally makes to announce movements such as "I'm jumping on the table now!" The eh, eh is the noise he makes while watching birds (and twitching his whiskers).
I used to have a cat who growled in her sleep. Sounded just like the Doberman.
Otherwise, my cat just walks around saying, "NO!!!" It's the Siamese.
"Are you a good kitty?"
"NO!!!"
"Do you love me, kitty?"
"NO!!!"
"Is world peace attainable, kitty?"
"NO!!!"
He's pretty smart.