There is no issue with the car. Spoke to Audi who say it is normal and it’s the PPF Regenerative System. Probably cause by too many short runs. Same as the DPP on the diesel cars the newer petrol cars have the same regenerative process to burn off soot trapped in the exhaust system.
Irrespective of length of journey the cooling fan will run on for exactly 10 minutes when engine stopped. Also noticed that Start/Stop system not operating and also when aircon switch on warm air is blowing out. Local Audi dealer says no fault shown on diagnostics but this does not appear to be normal operating.