Something to think about, if it's NOT play growling, by taking away what he has for growling, this can backfire on you and make him take that one step forward into a bite. However, you dont want him growling everytime he 'has' something either.
A non playing growl is a prelude to a bite. It's a "warning", he's being possessive of whatever he has and doesn't want to give it up.
With that, try trading up for something more valuable...if he has a toy, start working on him to "drop it", and TREAT him for that toy. (Food is usually much more important and valuable than a toy)..
Work on "leave it"...set a toy on the floor, if he goes for it, cover it with your hand, "leave it',,when he leaves it, isn't going to touch it, TREAT HIM!! ..GOOD BOY!
If he is continuing to growl/possess things, well he wouldn't have them in the first place..
Have you thought of going to an obedience class?? very helpful for YOU and the dog