That is progress and progress is good.
Most likely that is the friction material starting to fail and it grabs causing the chatter. You can try a trick that works about 1 in 4 tries by adding friction modifier to the unit.
This is actually for rear ends but it basically softens the clutch material so it stops chattering. I included a picture of what it looks like. You just add this to the fluid and then drive the vehicle about 100 miles to work it in. It may not clear it up 100% but it will most likely improve it.
If the band was too tight then it would jerk or not shift properly. Chatter is most likely a clutch that is not slipping properly.
I know if sounds odd but I have Chrysler dealers add this to transmissions all the time and it doesn't harm anything except on the newer transmissions. However, on RFE units it is just fine. Don't add more then one 4 oz bottle or it could dilute the fluid.
Image (Click to make bigger)
Saturday, May 1st, 2021 AT 6:21 PM