Does it rattle as in it wobbles around and makes a noise...? or
Does it rattle as in it makes a noise as it vibrates...?
Wont probably be any help, but:
My gearstick also makes a noise. The best description i can think of is it's like a small ball bearing is vibrating in the bottom of a glass jar, but it only does this at certain engine revs, when it makes the gearstick vibrate at a certain frequency. I have no idea why it does it though.
Will be interesting to see what suggestions other members may have....