Our ds has popped and cracked since he was in-utero. I talked to the MWs about it and was assured it was just another regular "thing". He cracked from birth -4 months a lot. We also talked to our crunchy x-ped (long story) about it and got the same response. I haven't run across any research that says it's a red flag for anything. He has cracked less and less as he's gotten older, but every now and then his little back lets out a very audible crack.
I don't know if this helps, or not, but husband is 26 yrs old, and hestill has cracking and popping joints. It's really funny, I'll be playing the piano, and he tries to sneak up on me, and *pop* I say "hello dear" and he says "darn joints!!"
His mom says it heredetery. It doesn't hurt him. It does sound weird though.
I asked my chiro and he said it's normal because they have not developped their ligaments ( I think it was ligamtns he said) yet. Or at least they are not as strong as with older children thus pop easilly.
Thanks mama's, phew! I know, 3rd kid, why am I panicking?? (Uh, anxiety anyone?) He didn't seem to pop so much before, just recently he's been popping more. He has his 4 month appt tomorrow (at almost 5.5 months ) I'll ask about it. I also have a chiro appt this afternoon, I'll ask there to & I'll ask for an explanation.