Ear rings in a storage compartment? - Call Supercheap. Sorry Mate couldn't resist
Can you replicate the rattle when stationary? Or get your hands on a stethoscope or similar and sit in the passenger seat while someone else drives. I kid you not, I've done it and this does work for those hard to find gremlins. Like I have said previously rattles do my head in!
When you take it in for the 3K checkup, make sure you drive in the car with them, on appropriately rough roads to ensure they agree they can hear the rattle. Otherwise you'll probably get it back with a "road tested it and could not hear the rattle".