Just had the 1000km service done, the bump noise coming from the tailgate is the lock resetting itself, only occurs when raising the tailgate, so that is that problem solved.
Told then about the bad knock coming from either the tailgate (which was ruled out above) or the rear suspension. As soon as I said this the service fellow suggested it would be the rear sway bars. Picked the car up and they had tightened the rear sway bar, noise gone!!!