Sounds like a problem I just had about 2 weeks ago.Had a little rattle up front on rough dirt roads and thought it might just be my pins on my brake rotors allowing them to rattle a little.(By the way I have a '91 Legacy L Wagon 221,814.)Then I started to get a pretty severe shimmy and I recognized it as my ball joints.Changed them both along with new brake pads and a good greasing of the CV's and now its fine.I also think I'll be needing tie rod ends soon as they seem a little loose for my liking.Jack it up and pull the tire.Place a large srew driver between the lower arm and the spindle and pry up and down.Watch for any movement.If it looks loose replace the ball joints.About $38 apiece here at Advance.Good luck.