I've heard Macs making this sound - basically sounds like the hinge is "Sticking" and breaks loose.
I've not known it to cause any problems, so if it's out of warranty I'd just let it be. If it's BRAND new, it may sort it on its own as it's used more. Even so, if it's a covered Mac (warranty or AppleCare+) I'd certainly consider bringing it into a store to be evaluated.