Bought my 08 last year with 30000 miles. Went to the dealer for this same reason. They told me it was normal. Look up unabomber manifesto on trannies.
The tranny for the 08+ are from the lgt and have straighter cut gears for 1st and 2nd gear to make them tougher but they whine more.
Go on youtube and search for 08+ wrx 0-60. Check out the vids on how the trannies whine in the videos
Its all normal