If the issue is caused by a worn wastgate replacing or repairing the turbo should help. However if it's due to exhaust design and tune then it probably won't help. If you have a complete stock exhaust system and tune it's more likely wear and tear.

Something I found while searching, The 4th post by Edmundu somes the issue up well.
http://legacygt.com/forums/showthrea...ter-47980.html

I imagine changing anything will change the way boost behaves in the car and it'll just move the issue to a different rev range. So I'm not too inclined to try fixing it till I'm ready to take it back to the tuners, they seemed to think it's not a big deal anyway. I couldn't hear it at all before when I was on the stock exhaust and stock tune.