Clio III blower/air conditioning stinks

Hello dear Motor-Talk Community, I hope you can help me, I am already in despair I have a Clio III year 2005 and have a problem with the ventilation. The problem is only since spring this year. If I drive my car for a time and then turn off, and then for example half an hour later start the engine again and start driving, then the ventilation starts for a short time ( 2 – 3 minutes ) pretty much to smell, so I have to open the windows because of the smell. However, after a few minutes the spook is over and it no longer stinks. It is both when the air conditioning is on and when it is off. I hope you can help me please, maybe someone has already had a similar problem. Thank you and many greetings! Florian