Strange sound coming from front left of engine bay

Every now and again I hear a sort of squeak like sound coming from what sounds like near the left wheel. The cars a 3rd gen Legacy B4 twin turbo. I understand there is a BOV in that area that has something to do with the TT setup which it could be but i'm not really sure. The sounds seems to happen completely randomly so i'm not so sure thats what it is. any other ideas?