No it is not my farts. I turn the heater on and for the first minute to two minutes it has a musk like rotten eggs, what could this be?!

Also, before it got cold if I had the fan on with the windows up and I wasn't moving, I'd get an exhaust smell coming in through the vents. When I'd start moving it went away, or turn the climate control to recirculation mode it was fine. That's not a major thing, I'm just worried that the rotten eggs smell means something worse like a failing catalytic converter or something to do with the cooling system. The smell only occurs when turning the heater on.

 

I'd start by changing the pollen filter & check for mouse nests while you do.
'Ozium Original' spray is very effective.

 

I'll check it but I'd hope its not the cabin air filter, I changed it as soon as I bought the car. So the new one has <600 miles on it.

 

This stuff worked well for me.

 

+1 mouse nest in air filter. Happened to me.