I may need refreshed on everything with you car, but did the noise happen after the diff was swapped, and I mean like you drove it a short time and then the noise came on? I would check for codes and see if you have one for incorrect ratio or max adapt shift. There are a handful of causes for noise on the converter side of the trans and they are mainly bearing noises, but since you mention the noise didnt occur until AFTER the diff work then it could be the pcm commanding max line pressure which will cause the pump to whine.
