Leaking Smoke

The exhaust fan grill will eventually face load and restrict airflow to the point that the intake fans will pressurize the interior, and smoke will start being pushed out every crack in the machine. The exhaust fan moves more CFM than the intake fans so as JB said there should be negative pressure in the machine. You can easily clear it by poking the buildup with anything that will fit the holes in the grill, and suck it out with a shopvac from behind. It is essentially ash.

Just as my warranty was about to expire, the exhaust fan developed a hard vibration So I was compelled to remove it thinking the fan was bad. It turned out the fan blades were imbalanced from buildup. While I had the left side of the machine open and the fan out, I decided to remove the fan grill and eliminate the maintenance of cleaning the fan grill. Removing that obstruction also increases airflow.
This is not an official recommendation. You don’t want to do that if you have any warranty left.