Burning smell through vents after 20 min drive

[PaulNYz]

So I originally thought I was burning the clutch.. but this smell just doesn't seem like clutch.
I ruled out the clutch because I get no smells whatsoever during the first half of my commute, which is going through a small section of lights before getting on the highway, and before the car is warmed up completely.

Once at operating temp, when I get off the highway and sit at a light, that's when the smell hits me through the vents. When I start moving again it completely goes away. I rarely operate the clutch on the highway, only ever shift between 5th & 6th.

There aren't any plastic bags on the exhaust system either. Perhaps engine smells? Some kind of crank case breather?

Anyone else have this issue?

P.S.- I only have a few months of powertrain left. Doubt this is covered by anything.