If you mean like 20 seconds after you start the car, and the engine/coolant is not even warm yet, then that should be some electrical gizmo. Some electrical things like for cold engine start would only be activated if the engine is cold.

See if the smell is also there when you first start the engine after it has been warmed up.

Also try just turning on the ignition, but not starting the engine. See if you get the smell.

And another factor is if the outside temperature is near freezing. Things like the side mirrors will automatically turn on to defrost. But they will not turn on when warmer - like 40 degrees F. Is it cold outside when this happens? Does it happen when warmer? Maybe the smell is a mirror?