Gelding's hip makes a popping sound

I have a 2 yr old gelding that I've had since he was a yearling. About 6 months ago I noticed a popping sound coming from his hip/pelvic region when he walks. He doesn't seem to have any discomfort and I haven't noticed any swelling, just the popping noise. Someone told my brother that he was going to be a big horse and he would grow out of it. (I don't believe that) I was told by an experienced horseman whom I trust that if it is a problem in that area that it's quite possible that he wouldn't be suitable to ride and might not even make it through 30 days worth of training. If anyone has any advice or info on this, I'd love to hear it.
I also have a yearling half brother to this horse and I think I've heard the same popping sound from him.

I have a Off Track Thoroughbred here who has a clicking/popping hip. His popping is no doubt from old racing stress, however he is 100% sound to ride, he has been over jumps, on extensive trail rides etc. I wouldn't push him into eventing, racing, barrel racing, high jumping etc but he is sound and may never have a problem with any type of riding.
With your younger horse its much harder to say. He could have done something as simple as fallen in the pasture six months ago being a young boy and knocked himself out of alignment! I would look into a vet check and a chiropractor visit before making the "he is useless" assumption judging on someones guess no matter how reputable. A great natural barefoot farrier can do wonders on funny joint clicks and pops also.

Sometimes a poped stifle makes that noise. I really don't have any experience with it, I just know that a horse at my old barn have a popping, and he was popping his stifle out and in. Try putting your hand on his stifle area, and see if you can feel a popping in and out.

I don't see why a funny noise means the horse is forever useless. That's nonsense.
While popping noise could be different things, he could just need to take it easy. My knee cracks when I rise from a squat, but I'm not useless and it doesn't hurt. =) There are a lot of moving parts, horses and humans are machines and those parts rub and pop, and if you are worried that he's hurt somewhere, have the vet do an exam. Many times some careful warming up and exercise will be the prescription. He's young, could be he's just not using himself properly, or he could need a chiropractor, but again, if he's exhibiting pain, call the vet!

My gelding (however, he is old) has a click in his hip because of arthritis. It could be something similar to that.

Id get xrays done.

I always err on the side of caution :)