Head rest rattle / vibrations

[M.A.94]

So my 16 year old w210 has very irritating vibration noises coming from the head rests when going over bumps or rough roads. I know this is no surprise from a car this old however I was wondering if anyone has ever rectified these noises and how?

At the moment I have temporarily got rid of the vibration using tissue to wedge inside the head rest, however I was thinking of replacing this with carpet underlay.