USRG Neck rattle
Since it doesn't actually have a "truss rod" per se, the steel rod is actually acting as the neck, absorbing all the tension. You can almost consider the neck itself there for your enjoyment, because it would be awfully hard to play a steel rod. Since the rod flexes independently of the neck, there can be creaks and rattles as they touch. I took mine apart (side allen bolt out, neck allen bolt out, nut connection plate out, remove headstock by pulling it) and coated the rod with linseed oil. I debated between that and something thicker like car grease. I wish I would've used the car grease because it would last longer in there. Anyway, When I put it back together the noise was 100% gone. *It was the rod and the wood creaking like a door hinge. If it's rattling when you play certain notes then you have to figure out a way to keep it put. Even then, a thick grease should absorb that too.