Our Jack begun growling

Question
Our 2 1/2 yr old male JRT has been the sweetest, loyal and submissive li'l guy.  Lately, he's started to growl at us on occasion A low steady growl. Sometimes it's when we pick him up, sometimes when he's sitting next to either one of us and the other comes by to pet him. He also looks like he can't help it.  He growls but he's also shaking with his ears pinned back. No biting, no snapping, just menancing.  He's also seems to be marking the backyard more and he's starting to hump legs and fuzzy slippers.  He's not neutered and we figure this is all related. We'll be having him neutered very shortly.  But, is this growling all part of the testosterone, or is there more to it, like dominance issues?  The poor little thing seems so scared and guilty to be growling yet does it anyway.  Your thoughts?

Answer
Hello, Neutering will help the JRT is a very dominating little dog don't be fooled submissive but dominating its an odd package but thats why we love em', Check into my Behavior and Dominance page on my website for some more info on what he is doing means: http://www.freewebs.com/dustycovens/behaviordominance.htm