I just want to say that it isn't a catch all to just do the coupler everytime there is a rattle. I have the snout bearings going out on me and also needle bearings will cause a severe rattle. (I have replaced the coupler and still have the rattle so I am experienced on that one ).
But for 99% of the time the coupler is usually it. Pretty easy job to do on both series one and two. Easier on series 2 gen 3s, but you could do it.