puppy growling at night

It is very likely a behavior associated with his heritage.  This is a working dog mix.  One intervention is to consider consistant, positive obedience training and practice.  Another is to use redirection.  When he growls, say his name (to get his attention) and change directions away from what has triggered his reaction.  The focus should be on you.  The dog will be adequately intimidating to provide you security and protection.  A very well trained dog will often be considered a risk because there is  every chance you have taught them more than the leash manners etc.  You need to use changes in direction and commands he can easily follow (like a sit).  As time passes, you will not need to move as far from the distraction, nor even change direction.  You just have to do it consistently enough the dog learns that distractions means concentrate on you.  Both of you will be safer.  Your dog will not be viewed as a threat by famliar neighborhood folks and strangers will see a big, black, well trained dog.  Nice deterent factor.