I have a problem with a blend door motor bracket that has broken. It started making a loud noise intermittently but now does it every time I start the engine. I found an article explaining what has happened:

A5 heater 'banging'.. The fix... Pics inside.. | Audi-Sport.net

or

Audi A6 2008 HVAC noisy flap repair. - YouTube


I need to remove the heater case from the heating duct to remove it, unfortunately neither of the two links shows how to do this and I am starting to struggle. I understand that the heater duct is locked in place by a white plastic sliding clip (at the top of photo)to the heater case. I have released this but the heater case still will not separate from the heating duct any suggestions would be gratefully appreciated. (I have removed the blot at the bottom of the heater case)
Heater case.jpg