Thought I would forward an update, as this has been quite an odd experience. Noise progressed into a "gravel" sound when reversing and moving forward under 10mph, then a loud screech, followed by was sounded like metal rubbing on metal. Upon getting off the freeway last friday (thank god), i was approaching a stoplight at about 15 mph, then suddenly felt a hard thump under my seat and heard a loud bang. Proceeded to move forward into the closest parking lot and the car began shaking violently. It sounded like a codswalloping chopper. Any way, long story short.. sound WAS drive shaft related. Sitting at subaru waiting to hear back. Likely a broken u-joint. So Sooberroo, congrats. I'd say you've got quite the ear! Thanks to everyone who contributed to this post! I'm just an average female hoping to learn a few things about her car!