I think it's the end links, lots of people have had that problem (I'm currently having the same problem and have been checking EVERYWHERE) from what I can tell it is slowly getting worse, tried tightening the end links today since a friend of mine said that fixed the problem on his… didn't help: I'm going to bring it in to Subaru (if they'll look at it for free even though it isn't under warranty) and hopefully they can give me a definitive confirmation of my suspicion…
EDIT: By the way @
slyphen since it's been over a month… did you find out what was causing YOUR problem?