I had a rattle in my rear door, and found that there is a plastic surround that covers the back of the electric window switch (to protect from water I suppose). It is just held in by the force of the door-card and window switch, against the metal of the door, with no catches or screws. I used a little double sided tape to hold it back.. No problems now!
Getting to it should take you no more than 10 minutes, I can do it in 2 with all the practice I've had..!
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black