It just started a couple days ago. It sounds like its coming from the front driver wheel area. When the car is in reverse or when in neutral coasting backwards down the driveway, I hear a metallic rattling sound. When I have the car in drive, at any speed, going straight or turning, there is no sound.

any ideas?

I cannot be 100% positive, but I had a similar experience with my Audi 5000 many years ago - Turned out to be the wheel bearings. Perhaps you could start there?

is it possible for a wheel bearing to only make a sound in reverse? and it went from no audible sound to loud within 2 days.

ok, so I went outside and jacked the car to manually roll the wheels, and I didnt hear anything. I drop the car and drive in reverse and now the sound stopped. It happened yesterday and twice today... and then nothing! I dont see how a sound that loud could just fix itself, but Im stumped. And its kind of difficult to diagnose when its not happening.

strodda: I was about to correct my post before you replied. It was not the wheel bearings on my old Audi - It was in fact the CV joint (CV boot). It cracked open and the bearings inside came tumbling out. My understanding is that with a bad CV joint yes you can get the sound to appear only in reverse. TEST: Put the car in reverse and then turn the wheel and drive around in a circle while in reverse - If the sound gets louder it is usually an inidcator of a bad CV joint.