I had a similar rattle/knock after I picked up our T6. I traced that rattle to the awning arms knocking against the casing. After reading a post about how it is possible to adjust these arms by loosening/tightening the upper nylock nuts on the vehicle end fitting I managed to cure it. What I discovered is that when retracted the arms need to come in contact with the four little rubber buffer pads in the centre inside of the casing. They are presumable there to kill this sort of knocking. I have just done a quick search for the post but cannot locate it at present. It was posted by either Daveyboydanger or Rhyddin who had worked on this issue together.
The awning can also work loose and rattle. Just a quick nip on the winding handle will cure it but don't apply a lot of pressure as you may strip the nylon gears inside the awning gearbox.