Rattle in the vents

Hi! My car is a 2003 PT cruiser standard, 4 cylinder, about 60,000 miles.

A few days ago, I turned on my heater, and it sounds like something got stuck in the vent.A clicking noise that clicks faster and faster the higher I turn up the heat (does this with a/c too, doesn't matter). I was hoping that it would dislodge itself when I turned it up to full blast, but it's still there. To me, it just sounds like I have something stuck in the vent, but I don't know how complicated it will be to fix. Can you help?