Oooo....YAY!!! That's a great sign! :D
Do not candle. If you do and the duckling dies in the shell you will feel terrible thinking your actions responsible. It is very hard to assist an egg in hatching if you're not very experienced and even if you are. Most ducklings/chicks that can not pip are just too weak and do not have a great chance at survival anyway. But..., look through the window closely. Many times pip marks look like bumps on the egg shell and not a hole; at least they do to me when the egg is in an incubator and the egg can't be seen close up. You can also tip the incubator just a bit so the egg turns and you can see the other sides. DO NOT DO THIS IF YOU BELIEVE THAT, IN YOUR CASE, THE EGG COULD BE DAMAGED IN SOME FASHION.