I have had dobe pups in the past but my most recent has been quite the vocal / biting little monster (I say that with love.)
Desperate for an affective way to avert his biting I hired a trainer. One thing he told me that was key in getting Doc to stop biting / nipping was to not engage in any physical activity with him when he started biting... meaning don't hold his muzzle shut, don't scruff him by the back of the neck but to make a sharp, high pitched sound then give him a toy. If he doesn't accept the toy and insists on biting, then to stand up and end play time or to walk away.
This has worked for me.
In the past I have always had success with the sharp, high pitched noise and re-directing the biting but what was absolutely essential with little guy was the lack of touching or physical contact. I had problems with him producing a demanding bark to try and get any response from me, be it negative or positive and passive dominance (ignoring) worked for a while, then he started biting. I would just stand up and walk away. Eventually he got it. I must say that I was skeptical, but after a few weeks he really got it. Now on occasion he will bark and I will just give him the stink eye and he grumbles and walks away from me.
So to sum ALL of that up, if your pup won't' stop biting, abstain from any physical contact when the "bad" behavior is being observed. Some puppies get riled up by being touched!
As far as the growling goes, I would not be afraid! Some of my dobes were very vocal and insisted on growling while playing, especially tug of war!
If you really don't like it then I would try and find a trainer who can help you correct it. I honestly wouldn't know where to start for that.
My pup is VERY vocal! He is always growling, which I call "grumbling" and will often do it if you talk to him. I would definitely not consider it aggressive in anyway!
I wish you the best of luck! I love puppies but MAN are they A LOT of work!
But it's well worth it
Oh... on a side note, my pup's trainer said we could spray bitter apple all over our hands and arms to see if that would help deter the biting... we didn't have to go there but I just wanted to throw that in for you.