Irritating rattle by rear heater control/vent/blind Any cure

[MickyBlue]

As per title, my rear passengers are on my case about it. :boohoo

If you tap the trim panel just below the vent outlet it's easy to induce. My suspicion is its the blind roller, or part thereof.

Is there a simple cure or is it a dealer job? I have tried with fingers to get the vent outlet out with fingers (to see if somethings loose behind) & I can nearly do it but need my trim tool which is at home, any advise welcomed.
TIA
Mike