Knocking noise coming from dash?!

[floyd 1.8 turbo]

Evening all,
My wife has a 2008 A4, 2.0 diesel. There is a knocking noise coming from what seems to be the top/centre of the dash which is very annoying! It doesn't knock all the time but when it starts it's quite a regular pattern until the cars switched off.
Any ideas of what this could be?

Many thanks

 

[Zafi]

Heater flap motor slipping?

 

[floyd 1.8 turbo]

Is that a common fault? It sounds like that could be it, sounds like it builds up then slips and knocks if that makes sense

 

[Zafi]

Press the off button, see if it stops the noise.