says "headphones" when volume is changed even if headphones aren't plugged

When I listen to my ipod with headphones it works fine, and sometimes (although it's becoming more and more rare) i can get sound out of the speakers, but most of the time it says "headphones" when i change the volume even when they're not plugged in. The ipod is less than a year old and i've never dropped it or gotten it wet or anything like that.