I would try to take out any blockage.
Use a wire- like a chunk of coat hanger- and bend a hook in the end, then poke it in through the opening and see if you can catch hold of anything. It's perfectly safe to do this, as long as you're not smoking or trying to see by the light of a candle or something.
( The Resident Loon Not a demographic. Do not measure., Wed 13 Aug 2008, 13:11, Reply)