Check our spoke tension. Pinging could be a sign that your spokes are moving around too much because of loose, under-tensioned spokes. A good LBS can check the wheel for you and have it re-tensioned if needed. Or,......you can do it yourself if you are willing to learn how to tension and true wheels. But remember that you cannot take too many chances with wheels, so it's worth the time and money to keep them in good shaped.....