Took off the grill yesterday to see how hard it would be to make my own grill and mount it without modifying too much existing stuff... and I noticed 2 plastic 'box-like' items on either side. They are just below (attached?) to the air intake nozzles. They have an opening in front and if you stick a finger in there you can feel a flap. Does anyone know what this is?

Was thinking of modifying the plastic intake part to enlarge it or to fit cone filters up front if/when I make a new grill, but I didn't want to mess with that plastic box until I know what it does.