I have the exact same noise, but only in 5th gear around 3k rpm down. It's a stock IX MR and all fluids replaced. I have taken it to a dealership to no avail. However, I was told to come back by next week on Tuesday to test drive a similar vehicle for further diagnosis. Why Tuesday and not on the the same day? Similar car getting a brand new engine and wont be ready till then.

They were not sure what it was. I kept pointing out to them that it's the TC or possible Diff. You can hear in on the driver side section then it would travel down to the back end side once you have reached 2k rpm under deceleration. My take is that the sound travels from the front diff along the driveshaft reaching the rear end side.

Anyhow, I will keep you all posted. Keep this thread open and make sure to post once you get it fixed.