my son is 6 years old, 50lbs. and his neck starting making a popping noise when he leans back his head (looks up). it happens every time he tilts his head back and sounds like a disjointed sound, not a neck cracking sound. he has had a five view x-ray done, which appeared normal. my son says it feels like he needs to pop it. Just in the last 2 weeks, he also has started over extending his left arm. It does not make any noise, but he says it needs to pop. The inside of his elbow bows when he extends his arm. One evening he complained that his knee hurt when he was trying to run. Are there any bone/joint conditions that he could have or any diagnostic testing that I should seek out for him? his pediatrician says popping without pain is considered normal, but I have noticed a progression of symptoms. Should I take him to some one, like an orthopedic MD? Thank you.