Jed, can you tell us the growing conditions for your plant? Maybe we can figure out if the problem but I would suspect it is nothing to worry about if you can't see any insects. If there is any possibility this could be a fungal infection try rubbing Cinnamon all around the wound. Cinnamon is a great anti fungal for aroids.

Knowing about your soil mix, the temperature and humidity the plant is grown in, the type of light used and how often you water can be helpful.

The link below may help as well.

Here is a link that might be useful: International Aroid Society