I know the answer everyone! Mine too is having the same issues. It is in the transmission. Specifically the torque converter/input shaft. You need to make sure you have new fluid in it though because deteriorated thin fluid will exacerbate this issue. Also if there is an excessive amount of clutch material in the pan you might as well rebuild because to fix this issue you have to get the transmission out of the car anyway.
Personally after my second or third drain and fill if it continues, which it has already improved drastically btw after one....I’m going to drive it till it goes then performance build it for relatively cheap.