Your baby suddenly sounds like a pint-size sawmill: Don't panic! About a third of kids grind their teeth at some point (it's called bruxism)—especially when their front choppers start to cut through around 8 to 12 months. Rubbing those sharp edges together helps relieve painful gums. It could also be a learning process: "Having teeth is a new sensation," says Jeffrey Janoff, a pediatric dentist in Venice, FL. Grinding's one way a baby can explore what they feel and sound like.
Almost all babies outgrow the habit. Until yours does, you can give her plenty to do and look at and offer her a chilled teething ring. If she's still grinding after all her teeth come in, have a pediatric dentist check them for signs of excessive wear.