Is Stormy just letting you know that he wants interaction on his terms,this would be quite normal in an adult grey.It sounds like you can handle him quite well when he wants.I would take notice to his body language and react to it,if he wishes to move away from you let him, Come back and try again later.Some greys do growl, this usually means they are very unsure of what is going on and scared.Stormy was not socialised as a baby and been in a few homes so also may be feeling abit insecure,some greys are like that.As you say you have come along way so continue what you are doing but my advise is watch the body language and back off if he is giving you signs that is what he wants,and take advantage of the times he is receptive to contact.Good luck.