so the other week when i was driving on a private road that was closed off

and stuck my DSG into 'S' and put my foot down for a bit after i slowed down i noticed a noise coming from, well, at the back of the engine or under the dash? then happened again the other day with a friend in the car who heard it too and said could be drive shaft. It only lasted probably a couple of minutes as i slowed down. any ideas what this could be??
cheers