Have just checked two other (basic) trailing sockets I have (under the bed, feeding side table lights) and YES, they rattle as well (?)
So I took out a screwdriver and opened then up ........................ the culprit .......... a loose or weak spring which help keep the sliding internal socket covers in place (the internal cover that stops you sticking anything in to a socket?).
As one of the small springs was not doing it's job, one of the covers was moving within it's slots ..................... took the spring and cover out ................ put the socket back together and rattling has now gone!