On my car, I notice a whirring/whining in park, drive reverse or neutral but I think it is the transmission pump or torque converter I hear. It is not loud but I can hear it outside the car. Since you only hear your noise when driving, it has to be something after the transmission. Carrier bearing is a good start.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge