When I start the engine in my 2018 plate fiesta there is a creaking/groaning noise from what I think is the vents in the dash. If I change the vent settings I sometimes get the same groaning noise.

Can anyone shed any light as to why this is happening and how it can be fixed?

If you have climate control when the car shuts down the outside air is shut off by a flap. 

Then when you start your car up, the common noises you’ll hear are  depending on conditions, outside air may be restored to the cabin along with adjustments to the flap controlling air direction. 

It may well be something that you may decide to live with as I suspect even if you replaced the heater unit as soon as wear takes place that noises will return. 

43 minutes ago, Aldridge Andy said:

If you have climate control when the car shuts down the outside air is shut off by a flap. 

Then when you start your car up, the common noises you’ll hear are  depending on conditions, outside air may be restored to the cabin along with adjustments to the flap controlling air direction. 

It may well be something that you may decide to live with as I suspect even if you replaced the heater unit as soon as wear takes place that noises will return. 

Andy, thanks very much for your reply. Indeed I do have the climate control on - I leave it on all the time just to keep it running ok. As you say I think I will just learn to live with it.