Innenraum: Bad smell

[pepaaa]

Hi,

I was wondering if anybody could help me. I think I have a problem with the inner air circulation.

If I switch to inner circulation there's always bad smell coming from fan exhaust, as if I was driving behind 10 big lorries. It doesn't matter if the air quality outside is good or bad, it always smells really bad.

Normal air coming from outside is fine... I bought the car a few month ago. I had all interior/exterior air filters replaced at the same time and I don't know if it was different before.

Where is the air used to re-circulation coming "from"?

Please help

Greetings!
Pepaaa