The problem with my pup

[maryevaoh]

My 4 month old husky pup is amazing. He is calm (as long as he gets his exercise), polite, gentle with kids and cats, and quick to learn. He has one problem that I'm having trouble fixing, though, and that is growling at certain people.
The people he growls at tend to be tall, middle-aged men that he only knows from as visitors in places he considers his home. Now, he has never bitten, shown his teeth, or otherwise shown any aggressive behaviour to these people, he just lets out a low, almost bark-like growl, and will back away and come to me if they approach him. He will cautiously sniff them if they gently give him their hand, but he will still growl (it's more of a "grruf" kind of noise, if that makes sense) at them when they stand up, or if he wanders too close to them.
Now, this cautious behavior wouldn't be so bothersome if it ended after getting used to the person in question. But with a few people he's acted like this towards, he continues to growl anytime they come visit. Most of the people he's like this with are very good with pups, and have tried speaking softly to him, offering him treats (which he takes) and gently introducing themselves to him with me standing beside them, but he continues to do this.

Any advice? :P

Edit: Another issue that is hard for me to deal with is little Koru's insatiable hunger for cat food. One of the problems with this one, is that I am EXTREMELY protective of the cats, particularly the one that's mine (the three other in the house are my grandmother's), because I've heard the horror stories some people have about huskies and kitties (our other two dogs have disproved these, but it's still something I watch out for). This means that I get pretty angry when I catch him stuffing his face into the cat bowl, or jumping onto the counter to reach it, and the cat walking away giving me that "why do we have dogs, again?" look, and I have a hard time thinking of a positive method for punishing him when he gets to the food. I'm guessing the best way for me to deal with this would be to do preventative training, instead of punishing him when I catch him in the act, but I don't know where to start with this one.