Air vent making sound when outside air is flowing in on 2007 Pontiac G6

My car air vent is giving a weird sound like some stick or leaves are inside it and this sound is only occurring when outside air is flowing in
Any suggestions how to repair it or how much will it cost

2 answers
could be leaves trapped inside heater box have blower motor pulled and ck for debri.poss cost 1 hr labor
clear leaves