Your dishwasher drains and refills several times during a cycle. As it drains, the drain pump makes a snapping sound. This is normal and occurs several times during a cycle.
The sound could also be coming from the detergent dispenser lid if it has a hinged mechanism. When you’re opening the door, you may hear a snap as the lid is set free.
If your appliance isn’t operating normally while making this noise, contact an authorised service agent.