Like Jack said, you might want to wait until the builders warranty is just about to expire to have them come back and fix it. What is looks like to me is that whoever did the taping had topping mud in their pan and put taping mud on top of it, or visa versa, something to that effect, and when the topping mud got used it began shrinking back while the taping mud doesnt shrink. It looks that way to me because it isn't everywhere, it's just hit and miss, and it looks like you could even tell where the taper was when he filled his pan and what direction he was moving, as it tapers off and the spots become further and further apart, it's definitely not structural, tho, purely cosmetic. If you choose to do it yourself, it's pretty easy. you could take a razor knife and cut a small slice perpendicular to the tape line to roll the tape back and smear a little compound under the part that has released entirely, then just press the tape back in place with your taping knife, using the excess mud to skim and fill the surface. After it sets up for fifteen minutes or so, wipe it with a damp sponge.