Sorry to hear of your problem. Like you I've been lusting after a Mule.
I hope Robin Wales doesn't mind me posting the advice he used to give when he ran Busker Guitars. It helped me sort out rattles/strange noises on 2 resos I had, an MM Blues and Continental single cone.
A tech couldn't stop the rattle on the Continental - he put a matchstick in the tailpiece! Hopefully your tech will know more about resos!
http://www.buskerguitars.co.uk/3.html