If its slack in the driveshaft you will hear thumps during shifting ,clunks when putting into gear.The 2nd guess is it understands what you are about to do too it by tearing its soul out and putting it into a japaneze can.You may need a car whisperer to fully understand the 2nd guess.
Seriously though ,in most of these trannie noise issues a lift and a good tech with another person in the car for testing the noise out by having it in drive and reverse to gain its exact point of origin.