Hmmmm 
If you set the stop-bar slightly higher, does it still rattle?
Did you try touching the neck pickup while strumming to see if that was causing it? (encountered that one once, strangely enough)
Did you try strumming it while you were holding the adjusting wheels on your bridge?

If you set the stop-bar slightly higher, does it still rattle?
Did you try touching the neck pickup while strumming to see if that was causing it? (encountered that one once, strangely enough)
Did you try strumming it while you were holding the adjusting wheels on your bridge?