burning rotten egg smell when i floor it?

Hi All,





Just got a 325i 2002 automatic it just hit 134k. got it about two weeks ago.





Car runs good, kept really well.



however, usually when i floor it, the car gives this rotten egg smell from the vents.





Anyone know what this may be?



is it something that might be expensive to fix? there are no lights on cluster, car is clean tittle.