Rmlamp

I noticed this problem awhile ago in my '01, but nothing seems to be wrong as far as actual operation. Whenever I'm in gear, whether it be drive, reverse, 2, L my transmission seems to emit a light whining sound. So quiet that I can't hear it when in the vehicle. In fact, the only reason I noticed it was because I was near a wall in a drive thru and the sound bounced off the wall.

I did a fluid and filter change after noticing the noise, though it did seem to help, the sound is definitely still there. The old filter was really clean and the magnets in the pan were as expected. There seemed to be no significant internal damage as far as metal shavings. The old fluid was pretty red as well so I'm kind of at a loss as far as whats going on.

Has anyone else experienced this? Any ideas on what might be going on?