The trans shouldn't whine on acceleration. It sounds like a bad wear pattern on the gears. There is no good way to prove that there was abuse, it is all up to the tech and the service department on how they go about wording it. If your car is stock and you haven't had any issues with it, you shouldn't have a problem warranting it. I know we would probably warranty it here. I've seen a a few low mile 2011+ STI's come in with cracked ring lands and that was warrantied by us with no problem. Just go out of your way to be extra nice and not combative to the service department and that goes a long way. Hope it all works out for you!