Originally Posted by TerryJenk

Probably the Webasto heater ? There is a small exhaust comes out under the passenger footwell . Check if any noise from there .
It is used to assist in warming the car in cold weather . Though it can be reconfigured to pre-heat and defrost the car in cold weather.

Check these out .

xdrivers.co.uk • View topic - Got my webasto to work, hot air!!

xdrivers.co.uk • View topic - Parking heater remote start- Enabling