I know what you are talking about. I get the same thing happening to me, but it happens almost randomly. Its almost bothersome for me because i feel like i am just smelling the inside of my lungs through the back of my through.
Sometimes i worry about what it could be, but i try not to think about it. This is the first time that i have actually tried to find out about it and search online, but not one else, except you, has experienced the exact same thing as me.
Now you mention it I've had this too. I think it's sinus congestion that clears when you exercise so you smell it a bit.
I too want to know what that ammonia smell is when I inhale then exhale I smell it bad plz give feed bk .I jus noticed this recently.;0(