knocking noises from behind the cup holder

[pmeatonmobile]

I have recently bought a MB CLK 240 W309 petrol 2002 and have knocking noises from behind the cup holder next to the heater controls. I have removed the glovebox and found a control unit which operates a flap which i believe to be causing the knocking. This car has had a new battery fitted and the pollen filter removed. The sensor for the AC beneath the filter has become dislodged and fallen into the heater blower motor blades. Should I replace the control unit or the air temp sensor to stop this annoying knocking?

Any MD techs please help...