I have just sorted my boot rattle, it was the trim under the rear windscreen. I guess over time the clips holding the trim have become loose and it just sort of flapped about when going over bumps. Interestingly enough, the edge of the window on each side had the worst rattle.
I found some foam and pushed that into the corners, between the glass and the trim. I then followed the trim and created a foam layer between the trim and the window. It has completely sorted the annoying rattle, coudn't believe it!
