Does the belt have foreign material on it, such as oil, grease or coolant? Even though it is only a year old it can still be part of the problem. A good hard careful inspection is in order. I've seen a lot of nearly new belts squeel from someone getting carried away with belt dressing or grease. Sometimes a nearly new belt will need to be replaced and the pulleys cleaned. The problem can be as simple as coolant spilled on the belt.
If the belt checks out, then the tensioner is the next place I would look too.
