Growling dog!

My neighbors have 2 golden retrievers. They're are brothers, got them at the same time as puppies and are now 9 years old. Love the dogs and always go and say hi to them and play w/them when they're out. One of them however, will come over to me if I'm sitting down and of course, I start petting him. He's fine for a minute or two then will start doing a low growl. It never gets to be really loud and he never has snapped or tried to bite me and he always wants me to pet him if I stop. I have to admit though, that when a dog growls at me, I pay attention. His brother never does this and they would both be in your lap if they could. At first I thought he was just talking but I'm really not sure what is going on. Is it jealousy because of his brother? I've tried to notice if he does it if the other dog isn't there but where one is, the other usually is. I'm not really afraid of him but I certainly respect that fact that he is growling. Anybody heard of this?
Thanks!

It sounds like the one dog wants to be alpha over you. When you're sitting down, you're in a more submissive position than if you were standing up. He may be demanding that you keep petting him when you stop. If you keep petting him, you're letting him have his way. It might not be the case at all but that's what popped into my head first. When you see him again, you should make him work for your attention. A pat on the head requires a sit. A bit of playing requires a sit (or down or anything really). Everything he wants, he has to earn from you. It may be harder since he's not your dog but if you don't give in to his demands, things should go a bit more smoothly.

Oh, I just thought of something. The low growl could be a way of just saying he likes it. But either way, it wouldn't hurt to make him sit for a pat on the head.

[edit]Oops! Didn't see the reply underneath:p

he may just like you petting him and the low growl is his way of telling you i know that wolves and dogs are not really the same but wolves will have a low growl when they like something or as she/he said above he may want to be alpha

He will do this also if I'm just sitting in their living room with the husband and with there. He's done it a few times also when they both come to the fence and stand up to be petted but not as much as when they're either out of the fence or when I'm in their house. I'll try the suggestion about having him earn the affection. I've just never had a dog do this so not sure what to think.