How do I fix this basement gas smell?

Been living in a rented old basement for 2 years now with my significant other and we have ignored for the most part the smell of gas that I assume comes from behind a door in one of two bedrooms where the main gas connector is.

We smell it when entering the basement front door coming home from work. And then the smell just disappears. My Dad who visits every two weeks notices the smell too when he comes in.

Not sure if this might even be normal for a basement to have this level of gas smell. I know for sure lots of people live in old basements like this. I say old because the house is at least 40 years old but we have furnished it well enough to make it look nice and homey. What can I do to stop the smell-? Thanks.