Sure its the transmission? Could be the PS tensioner pulley or something around that area. Those do tend to whine on 420a's and they get worst over time from moisture, water, etc. anything that gets into the bearings. It's about $120 part from the dealership, I should know I've bought one and replaced it on the wife's car. I would make sure exactly where its coming from first, a sound you hear inside the car can be coming from anywhere.