When I took it to the dealership they immediately cautioned me that it may not be fixable because doing anything to the headrest posts impacts the safety restraint system. I've taken this all the way to the service center manager and had a NEW seat put in just last week. Guess what? This one rattles too -- same problem. Do you think the vibration material you're talking about will still work? I'm hoping some ofther folks can confirm this as a problem too (or not). Thanks.