The hinge is made out of aluminium, an all metal new redesign hinge, but since this new design is so thin, Apple need to separate the display module, which previously built into the hinge to make it thinner, so the display module now has been incorporated into the logic board. Therefore, flexi cables are needed to connect the display and the module. Try flipping to the back of the MacBook. You can see there's a gap at the hinge, torch inside and you can see there are 4 flat black flexi cables. When tilting or opening and closing the lid, the hinge's flat metal part actually will touches it. New machine with new cables (new cable is harder) will produce plastic sound (Flexi is plastic) when being flexed. As for your case, the cables will become softer after some heat and intense closing and opening the lid. So that can be explained why your creaking noise went off all of sudden by itself.