I just had this enlightening experience a few days ago. Everybody says that the cattle barn smell in the monorail cars comes from people's dirt and sweat. I never really believed that. How could every car on every train, that I assume is cleaned every once in a while, smell exactly the same?
I finally had my air conditioner serviced on my ancient 2005 Corolla with 221K miles. I'm older and fatter and can't accept not having a/c even in my spare car anymore. Every time I turn it on it smells exactly like the monorail for the first few minutes. Somebody else may have pointed this fact out but that monorail smell has to have something to do with the a/c and the stuff growing and blooming in there.
Strangely, I find it pleasant. I know many of you would understand.