Looks like a good starting point for fixing the rattles in my Impreza. Nice writeup.
EDIT: Also trying to track down a rattle that only happens during the summer when the car is idling, like at a stop like while still in drive with the A/C on.
Turn the A/C off and the car revs a bit higher and the rattle goes away. It's a pretty low rattling sound as well, and super annoying. '06 Impreza.