Volvo 240 transmission noise when first starting out

My 1991 Volvo 240 transmission (automatic Aisin Warner AW70) has started exhibiting a strange behavior when it’s first starting out in the morning. It’s quiet for the first 3-4 minutes and then when sitting at a traffic light it’ll make a faint intermittent whining sound that disappears when it’s put in park, reverse or neutral. It also disappears when the car starts accelerating. When sitting at a light after 10 minutes has passed its quiet and everything is normal. The transmission was flushed using the return line method 5k miles ago and the filter and fluid was replaced ~30k miles ago. I checked the transmission fluid and it’s still red and the level is good when I check it after driving for 30 minutes. The transmission also shifts incredibly smooth. Any idea what could be causing this whine or if I should be concerned?

Here are some videos of the noise in question.

Thanks
Matt