Ticking from vents

When I turn on the air conditioner in a 98 malibu I hear a slight ticking coming from the vents. It is more profound towards the passenger side. I know the blower motor is on the passenger side of the vehicle. The ticking is there with the ac on and off. What might the sound be caused by?

Possibly a leaf or something caught in the squirrel cage blower? Does it tic faster or slower when you change the blower speed?

Something may have fallen down into the defrost vents on top of the dash .The airflow is causing it to vibrate .

The sound does get faster with the higher speeds of the fan. How would I go about checking to see if something is down in it?

To get to the blower fan, remove the glove box. The fan can then be cleaned by lifting the cover and removing any debris from inside the fan cage.

Thanks to the people that helped me out with this. I finally got around to pulling the blower motor and it was full of leaves. After removing them, all the weird sounds from it went away.