What is this hole in the nose of the A330?
It is the avionic compartment access door as described in the Flight Crew Operating Manual!


  An inward-opening, manually operated, hinged door gives access to the avionics compartment. This door is in the lower fuselage, forward of the nose landing gear bay. A ladder is stowed inside the compartment adjacent to this door, which may be either be operated from the interior or the exterior.
  This compartment is also accessible from the cockpit, via a floor hatch located behind the Captains' seat. A fixed ladder in the avionics compartment for access from the cockpit.


Here is a drawing from the outside!



And here a view from the cockpit flight deck for an A340!