I now put household scotch around the white hinges to which the rear sits lock. I have also opened the armrest in the middle of the seat. I have then driven over rough road and I think the rattling has diminished considerably. Maybe the armrest was making the rattles. Anyway, the plastic cover behind it is very screechy.
Earlier I had my girlfriend sit in the back listening to rattles, but she did not hear many and could not place the ones she heard

Girls... I think she was not concentrating.

Will drive around and see whether I have fewer rattles now.