What is THAT noise? W203 C200K Coupe.

[Darzet]

Last night turned on ignition and moved off and could hear what can only describe as a TOCK every second. Almost like your grandfather clock in the hall.
Sounded like coming from behind the middle of the dash and maybe something to do with the vents - tapping the central vents with your knuckles make a similar noise.
Eventually went away after about a minute I would guess, and did the same this morning when I started up then went away after a short while. No warning lights on dash, but bleedin annoying and maybe expensive to fix?

What is it? I'm thinking it's related to the aircon /ventilation system?

Thanks

 

[AndyPCD]

It will be one of the stepper motors for the flaps in the heater box

Its quite a common problem on the car. Will need plugging into star machine to determine which one its is.

Some are easier than others to change. Some only need a few dash trims removed to gain access while others require the whole dash being removed.