Something is making a creaking / cracking noise behind the small vent on the dash. It sounds like a motor/gears not meshing any ideas?

Very much depends on what that noise sounds like. Might just be the automatic temperature control mechanism doing it's thing.

its loud enough to be intrusive when the car is ticking over...got no radio at the mo! (and the last car I had was a merc s class!) It sounds like cracking plastic or plastic gears breaking up and it is continuous never stops!

Sounds like the little servo motor that controls the re serk vent mine dus it, it creeks

Easy fix? or should i just get the radio working!

It's an air temperature sensor.
Take it out and clean it and it should stop making noise...at least mine did after cleaning

Cheers for that!