Since this is not the sound of the calipers moving inside the carriers when there is a direction change in the wheel rotation, I think it is excatly the little normal sound anyone gets from the DSG engaging whenever selecting back and forth from D to Reverse.
Thing is, since you guys are manual, the clutch will engage as the car starts moving (as opposed to immediately when you move the gear lever as is the case with the DSG), this is why u would not immediately associate it as transmission-engaging related and describe it more as a sound coming from when "the car starts moving".
Pefectly normal, and will vary depending on the oil temperature of the transmission.