C180 ticking after engine cutoff

[sceh]

2011 C180 diesel.
Yesterday I stopped the car,switched off the engine and for some time there was a ticking sound from under the bonnet. It was as though something electrical was running - not horrendously loud though. I didn't open the bonnet to locate it since I was struggling getting the car out of an icy place and had other things on my mind! Drove home and it didn't happen again. Next time I will open the bonnet and find out more but there are no warning lights or anything.
Any ideas I can probe before it breaks down on me?
Sorry for the lack of detail. I vaguely remember something like this on another car and it turned out to be the electric fuel pump but this is not likely here.
Thanks for any advice

 

[Bayleaf]

My SL 350 petrol makes a similar noise when the engine is turned off I think it may be the stepper motor in the throttle body returning to the start position. I had a Jag with a 2.7Ltr diesel engine and that used to do the same.

 

[Supernoodle]

Depends how long exactly it goes on for, but actuator end stop adaption (turbo, throttle and egr) happens at key off. It won't happen every time either.
During the adaption the valves are driven fully open and closed several times, hitting the end stops, causing a noise. Could it be this?

 

[markjay]

2011 C180 diesel.

I don't know where in the world you are, but just to say that in the UK with had the W204 C180 CGI petrol, and the W204 C200 CDI and C220 CDI Diesel, but not a C180 Diesel.

 

[sceh]

France. It is the same engine as the 220 CDI and 240cdi but has only one turbo

 

[sceh]

France. It is the same engine as the 220 CDI and 240cdi but has only one turbo

Actually they all have one turbo at least but the 180 has less power due to lower pressure or compression