Odd gear box sound D3 only

[PerArdua]

My 2015 Allroad was driven last night with the stereo off in town and suburban roads and I noticed that when the car selects D3 there is a noticeable change in sound, closest description I could add is it sounds fluttery, no loss in drive or any other outward signs apart from the noise and only in D3. Selected M3 and there is no noise until it goes back to D3. Is this something I should be concerned about?

[Elansear]

Hi I am no expert but it’s the same gear only the change points and speed of change would alter from D to M. Could it be engine noise relating to a change in RPM or road noise in D as the RPM will likely be lower.

[PerArdua]

I realise it is the same gear but in M3 the car isn't expecting to make a gear change and in D3 it is so I wonder whether it is something around the anticipation of making the change? I drove it yesterday in daylight and it seems like D3 is engaged for such a small amount of time in normal use and it is almost like the old gearboxes where the engine revs could rise for no increase in speed as the power was lost in the torque convertor. It doesn't affect the car driving and with normal noise in the car is totally silent, it is just probably heightened sensitivity to noise at night and driving like Miss Daisy, which isn't normal driving.